Seahorse Club
Aquarium & Livestock

Feed Ezy Frozen Mysis

Seahorse Club
Aquarium & Livestock

Feed Ezy Frozen Mysis

Seahorse Club
Aquarium & Livestock

Feed Ezy Frozen Mysis

Seahorse Club
Aquarium & Livestock

Feed Ezy Frozen Mysis

Seahorse Club
Aquarium & Livestock

Feed Ezy Frozen Mysis

Seahorse Club
Aquarium & Livestock

Feed Ezy Frozen Mysis

Black Slime

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  • #762

    Hey Pete,
    I posted the other day, about what I thought might be some sort of a black algea problem. Thanks for your response. I did go out and get the phosphorus absorption pellets, did a water change, changed all my filters and cut back on the feedings of the horses. Right now, I cannot seem to even make a dent in what might be the problem. I actually have come back into the lab tonight to run the water on the ion chromatograph. Following are the results:

    pH 7.7
    Nitrate 0 ppm
    NH3 0 ppm
    Nitrite 0 ppm
    Phosphorus 0 ppm

    The following seem disturbing……….
    Fluoride 25 ppm
    Bromide 458 ppm
    Sulfate 2500 ppm

    Any advice would be helpful…. the seahorses are still eating fine, but seem to be having some jerky movements. The tank also seems to have bubbles settling on the plant leaves that just stay…. and stay….. and never break.
    Thanks for your help!

    Pete Giwojna

    Dear Kris:

    Yup, I remember your earlier post. As I said, my best guess is that the black stuff is a form of slime algae or Cyanobacteria. It sounds like you’ve done a good job of getting your excess nutrients under control; zero nitrates and no phosphorus is bound to help in time. But your pH is too low (most seahorses prefer a pH of around 8.2-8.4) and some of the trace elements you listed are too high. Right now conditions in your tank seemed to be favoring the growth of that black slime algae for some reason, and if you can get your pH back up into the proper range, that may tilt the balance the other way and the black stuff may simply disappear on its own. Or its growth may be fueled by some of the trace elements in the tank (silicates, sulfates, phosphates, etc.) and it may eventually disappear once it consumes the available supply of one or more of those key elements.

    A pH of 7.7 is too low for your seahorses and may account for the jerkiness you have noticed recently, as well as possibly promoting the growth of the black slime. Do you know what the total alkalinity or carbonate hardness of your aquarium water is right now, Kris? What type of water are you using and what brand of salt mix do you use?

    For now, I would concentrate on the following: (1) raising your pH; (2) physically removing as much of the black stuff as possible if it is growing in sheets or mats; and (3) discontinuing any additives or supplements you may be using for that aquarium (trace element replenishers, foods for filter-feeding invertebrates, iodine, strontium, etc.).

    The main thing is to get your pH straightened out. Since you’ve been having trouble keeping your pH up, I’m going to provide you with some additional information below on key aquarium water quality parameters that should make the relationship between pH, alkalinity, carbonate hardness and calcium a little more clear. I realize that you will already be quite familiar with much of this material, Kris, but please bear with me, since some of it may be pertinent to the problem you’ve been having with black slime:

    Basic Water Quality Parameters.

    Ammonia (NH3/NH4+): Optimum level = 0 at all times

    Ammonia is highly toxic to both fish and invertebrates in even small amounts (> 0.01 mg/L or ppm). Causes of ammonia toxicity include: immature biofilter (new tank syndrome), impairment of the biological filtration due to antibiotics and other medications, overfeeding, overstocking and dead specimens that go undetected (Webber, 2004).

    Nitrite (N02): Optimum level = 0 at all times

    Nitrite is slightly less poisonous to fishes than ammonia, but deadly to many invertebrates at very small concentrations (0.01 mg/L or ppm). Even trace amounts of nitrate such as this can wreak havoc in a reef tank and cause serious distress to fish. High levels of nitrite result from the same causes as ammonia.

    Nitrate (N03): Optimum level = below 10 ppm in fish-only tanks; 0 ppm in reef tanks.

    Nitrate is the end product of the process of nitrification, formed during the Nitrogen Cycle by the oxidation of nitrite by aerobic bacteria. Nitrate is relatively nontoxic to fishes, but elevated levels (> 20 ppm) are stressful to seahorses over the long term and promote the growth of nuisance algae. Reef invertebrates can be much more sensitive to nitrate, and concentrations as low as 0.06 mg/L can cause problems for symbiotic stony corals. The nitrate level is therefore a good indicator of water quality. For best results, consider using live rock and/or a live sand bed (preferably situated in your sump) in conjunction with a good protein skimmer to help filter your seahorse setup. The skimmer will remove excess organic compounds before they enter the nitrogen cycle, and live rock and a deep sand bed will provide significant denitrification ability, all of which will help keep your nitrates down. Don’t overstock, don’t overfed, remove leftovers promptly (a good cleanup crew is useful here), grow and harvest macroalgae, practice good aquarium maintenance and maintain a sensible schedule for water changes.

    pH: Optimum level = 8.1 – 8.4 (typically fluctuates between 8.0 at night and 8.4 during the day)

    The pH is a measurement of the alkalinity or acidity of aquarium water. A pH of 7 is considered to be "neutral," neither acid or alkaline, while pH levels above 7 are considered to be alkaline or "base," and pH levels below 7 are considered to be acidic. Marine aquaria need to maintain alkaline conditions at all times, and low pH (< 7.6) is especially detrimental to seahorses because it is conducive to Gas Bubble Disease. Normal daily fluctuations in pH are to be expected in the aquarium, and are generally gradual enough not to be stressful (Webber, 2004). Maintaining a sump or refugium with a reverse photoperiod to the main tank can eliminate these natural pH cycles. Regular partial water changes are the key to maintaining stable pH. Buffers can also help but the hobbyist should beware that excessive use of pH buffers may increase KH values to dangerously high levels.

    Specific Gravity: Optimum level = 1.022 – 1.025

    The specific gravity measures the density of a your aquarium water relative to the density of distilled water, and aquarists use it to estimate the salinity of their aquarium water (Trevor-Jones, Dec. 2002). In effect, it’s one way to measure the saltiness of your tank, since the more salt that is dissolved in the water, the denser it becomes. This can also be done by measuring the total amount of dissolved solids in the water, which is expressed as the salinity in parts per thousand (ppt). Hobbyists must remember that constant evaporation of freshwater from the aquarium causes the salts to become more concentrated, which increases the specific gravity or salinity accordingly. Therefore, it is necessary to top off the tank with freshwater regularly in order to make up for evaporation and maintain the desired specific gravity. Seahorses tolerate a wide range of salinity very well and hyposalinity (specific gravity at 1.011-1.015) is often used to help rid them of ectoparasites.

    Dissolved Oxygen (02): Optimum level = 6 – 7 ppm

    High levels of dissolved oxygen are vital to the well being of both fish and invertebrates. The key to maintaining high O2 levels in the aquarium is good circulation combined with surface agitation (Webber, 2004). Wet/dry trickle filters and protein skimmers facilitate efficient gas exchange and oxygenation. It is important for the hobbyist to monitor the dissolved oxygen levels in the aquarium because a drop in O2 levels is often an early indicator of impending trouble — a precursor of problems ahead. A drop in O2 levels will tip off the alert aquarist and allow corrective measures to be taken, nipping the problem in the bud before it adversely affects his seahorses.

    Alkalinity: Optimum level = 2.4 milliequivalents per litre (meq/L), which is the alkalinity of natural seawater, is best for fish tanks; > 3.0 meq/L is recommend for reef tanks.

    The alkalinity is basically a measure of the capability of your aquarium water to resist changes in pH from the addition of acid (Trevor-Jones, Nov. 2002). Acid is continually entering the aquarium, primarily as the result of respiration (CO2) and metabolic wastes produced by the aquarium inhabitants (Trevor-Jones, Nov. 2002). The addition of these acids tends to lower the pH of the aquarium water. The higher the alkalinity of your aquarium water, the more resistant it is to such downward pH shifts (Trevor-Jones, Nov. 2002). The amount of buffers (primarily carbonate and bicarbonate) in saltwater determines the alkalinity, so the alkalinity in effect is the buffering capacity (Trevor-Jones, Nov. 2002). When the buffering capacity of the water is depleted, the pH becomes unstable. Alkalinity test kits can now warn of low buffering levels in time to prevent potential pH problems (Trevor-Jones, Nov. 2002).

    Carbonate Hardness (KH): Optimum level = 7dKH (the hardness of natural seawater)

    Carbonate hardness is another measurement of alkalinity. It is usually expressed in the German unit dKH (degrees of carbonate hardness) and is often considered to be the total alkalinity. (Dividing dKH by 2.8 will give you the alkalinity in meq/L.) KH actually a measurement of various carbonates and bicarbonates of calcium and magnesium within the aquarium water (Webber, 2004). Maintaining a stable KH is very desirable since it maintains the buffering capacity (i.e., alkalinity) of the system and prevents subsequent drops in pH. Aside from stabilizing the pH, reef keepers need to maintain KH and high alkalinity in order to assure that the calcifying organisms in the tank flourish. Corals and other calcifying organisms actively use bicarbonate, which is the main component of alkalinity, so the alkalinity of a tank with a lot of calcification can drop quite rapidly.

    Calcium (Ca): Optimum level = 350 – 400 ppm (up to 500 ppm in well-stocked reef tanks)

    Calcium is a very important element in the water in any marine aquarium and is a vital element in reef tanks. Along with carbonates and bicarbonates, it is required by calcifying organisms such as stony corals, snails and other mollusks, coralline, Halimeda and other calcareous algae, and certain sponges (Trevor-Jones, Apr. 2003). Calcium reserves must therefore be replenished on a regular basis. Regular water changes may achieve this, but reef keepers may require the addition of biologically available calcium to maintain adequate levels (Trevor-Jones, Apr. 2003). Seahorse keepers should be aware that brooding males provide calcium to the developing fry in their pouches, which the embryos probably incorporate into their skeletons. Deficiencies in calcium could thus adversely affect your seahorses’ reproductive success and the health of the fry. In fact, seahorses that receive a diet deficient in calcium often suffer from decalcification of their exoskeleton, a debilitating condition commonly known as "soft plate" disease (Greco, 2004).

    Phosphates (PO4): Optimum level = as low as possible in fish-only systems

    High phosphate levels are detrimental to marine aquaria. In fish-only tanks, they promote excessive growth of nuisance algae, and in reef tanks they also directly inhibit calcification by corals and coralline algae (Holmes-Farley, 2002). Phosphates arrive in the aquarium in fish foods, through tap water, as an ingredient in low-quality carbon and marine salt mixes, and primarily through the waste products of the inhabitants (Webber, 2004). Phosphates can be removed by using commercial phosphate-binding agents, but growing and harvesting macroalgae and protein skimming are the best ways to reduce phosphate levels

    Redox Potential or Oxidation Reduction Potential (ORP): Optimum level = 350 millivolts

    The redox potential relates to the degree of water purity in the aquarium, and can be thought of as a measurement of the water’s ability to cleanse itself via oxidation. It is measured in millivolts of conductivity, a unit that provides information about the reduction and oxidation characteristics of the water. ("Redox" is merely a contraction of reduction-oxidation.) Oxidation-Reduction Potentials (ORP) are closely related to the stability of the marine aquarium and can therefore be used as a barometer of water quality. Highly efficient filtration, good aquarium maintenance and management, and the use of ozone in conjunction with a protein skimmer will help to boost redox values.

    Seahorse keepers with fish-only systems need not be overly concerned about many of the parameters mentioned above, but I’ve summarized them anyway for the sake of thoroughness and the benefit of reefers who keep seahorses.

    As you know, Kris, the basic test kits you need in order to keep track of your key aquarium parameters are ammonia, nitrite, nitrate, and pH, plus a hydrometer to check specific gravity or salinity.

    Aside from these basic water quality tests, I also recommend that you use a test kit for measuring the dissolved oxygen in your seahorse setup. The reason for this is that a drop in the level of dissolved oxygen is a great early warning indicator that something is amiss in the aquarium, and can thus predict potential problems (and allow you to take corrective measures) BEFORE they become full-fledged disasters. For example, a drop in O2 levels could be an early indicator of overcrowding — a signal that your system has reached its carrying capacity. Or it may merely signal a rise in the water temperature due to a summertime heat wave or indicate that the tank is overdue for a water change and/or a thorough cleaning to remove excess organics and accumulated detritus. Or it could be telling you that your tank is under circulated and you need to increase the surface agitation and water movement. On the other hand, it can also alert you to a potential gas supersaturation event, which can sometimes happen if a faulty intake or leak allows air to be entrained in a pump.

    The point is that checking the O2 levels in your aquarium can alert you to impending problems and allow you to do something about them before they have dire consequences. A drop in O2 levels is often the first sign of a water quality problem and it can tip off the alert aquarist that trouble is brewing before his seahorses are gasping for air in obvious respiratory distress. Checking the dissolved oxygen levels regularly is the next best thing to continuously monitoring the Oxidation-Reduction Potential (ORP) or redox of the water, which is a luxury few hobbyists can afford.

    And if you’re having trouble with pH, you may also find it helpful to test the total alkalinity, carbonate hardness (KH) and calcium levels of the aquarium. Keeping the alkalinity and carbonate hardness at the right level will help you keep the pH in the desired range. A stable KH will prevent rapid declines in alkalinity and subsequent drops in pH. Your seahorses will benefit and maintain the pH in the proper range may well help you get the nuisance algae under control as well.

    In my experience, the best way to stabilize your pH at the proper level is to gradually adjust it upwards as usual, and then use a dual-phase or 2-part Calcium Buffer System periodically thereafter. This type of buffer has two parts — an alkalinity component and a calcium component — that simultaneously adjust the carbonate hardness of the aquarium as well as the calcium level, which is very beneficial for seahorses

    To adjust your pH to the proper range (8.1-8.4) initially, just obtain one of the commercially made products designed to adjust the pH upwards in saltwater aquariums and use it according to the instructions. Such a product should be available from any good LFS that handles marine fishes and invertebrates; they typically include sodium bicarbonate as their primary active ingredient and are often marketed under names such as "pH Up" or something similar. Just be patient when you are adjusting the pH and don’t add too much of the product too soon. Very often your pH won’t budge at all the first several times that you add the product according to directions. That’s perfectly normal, so don’t be discouraged if your pH stays at 7.8 even though you’ve added several doses of the product you obtained to raise the pH. Don’t don’t be tempted to add more of it or to add it more often than specified in the instructions. The product must first overcome the natural buffering ability of the saltwater in your aquarium before I can change the pH level significantly. It’s like performing a titration — typically, you add several doses and your pH doesn’t budge at all, but then the very next dose you add may change the pH dramatically. Since you never know when that critical point will be reached, remain patient and continue to carefully add more of the product as directed until the pH does start to change, and then adjust it to the desired level as gradually as possible.

    Once the pH has been adjusted to the proper level of 8.2-8.4, you then add the alkalinity component of the 2-part buffer system. Next you wait a couple of minutes and add the calcium component of the 2-part buffer system. Your pH should remain stable at that pH thereafter and this method also has the added benefit of keeping your calcium level in the proper range as well. For a typical seahorse tank, you can keep it stable at the desired pH by adding more of the 2-part Calcium Buffer System about once every week or two after you perform your usual water changes with the RO-mixed saltwater.

    The 2-Part Calcium Buffer System that Marcie and some of our other members report works well with their seahorse tanks is labeled "ESV B-Ionic" on the bottles, but Sea Balance and another of other brands do much the same thing. The alkalinity component of these two-part buffers maintains the carbonate hardness or KH in the aquarium, whereas the calcium component maintains the calcium levels in the proper range. Any good marine aquarium store will have a suitable product available for this.

    Siphon up as much the black stuff as you can while performing another water change, Kris. Try to gather up and remove any bits or fragments that may have been left behind (a fine-meshed net should what well for collecting up any the remnants). Discontinue any additives or supplements you may have been using for the time being, and consider using a small powerhead to increase the current and water flow in the area(s) where the black slime tends to grow. Keep working on reducing your nutrients and your hard work should begin to produce results eventually. Let me know if it doesn’t respond to these measures and, in that event, there are some other things we can try as well.

    As long as the gas levels in your aquarium aren’t supersaturated, those air bubbles you’ve noticed on your plants are not a cause for concern.

    Best of luck getting rid of the black stuff, Kris!

    Pete Giwojna


    Dear Pete,
    Thank you so much for all the information you gave me, reguarding my slime problem. I have tried hard to follow your advice and things will hopefully be getting better. I planned on running a tot. alk. on Saturday, but wasn’t able to and will do it tomorrow, along with the KH and Calcium.

    I am sad to say I lost one of my horses, but the remaining three seem fine and are acting normally again. I started with the 2 phase buffer and spent alot of time trying to scoop out the slime, which breaks up fairly nicely when trying to remove it. Its a mess!!

    To answer your earlier question, most of the water in my tank came from the Marine Store, as I usually buy it to start up a tank and keep 5 gal. or so on hand.(although, for this particular tank, I did make up about 20 gal. from tap water)

    Honestly, in all the salt tanks I have maintained, I have never had this stuff.
    Will it ever go completely away? It really is horrible looking.
    Thanks again for all your great help…. it’s really appreciated.

    Pete Giwojna

    Dear Kris:

    You’re very welcome to all I information and help I can provide!

    Your Marine Store should be a good source for seawater. I asked what kind of water you are using because one of the sneaky or hidden ways phosphates, nitrates, silicates and other undesirable compounds can enter our aquariums is through the tap water we use for water changes or topping off our tanks. If the water quality in your town is not what it should be, you may want to consider buying reverse osmosis/deinonized water (RO/DI) for your water changes. Most well-stocked pet shops that handle marine fish sell RO/DI water as a service for their customers for between 25 and 50 cents a gallon. If your LFS does not, WalMart sell RO/DI water by the gallon for around 60 cents, and you should be able to find a Wal-Mart nearby.

    Natural seawater is another good option for water changes. Like RO/DI water, natural seawater can be purchased at fish stores for around $1.00 a gallon, depending on where you live. It sounds expensive, but when you consider the alternative — paying for artificial salt mix and RO/DI water and mixing your own saltwater — then natural seawater is not a bad bargain at all. It has unsurpassed water quality and seahorses thrive in it.

    You should also be aware that freshly mixed saltwater can have residual levels of ammonia, but if you aerate the newly mixed saltwater for 24-48 before you perform the water changes, the ammonia will be dissipated.

    Along with low pH, dead spots and low flow areas favor the growth of nuisance algae rather than coralline or macroalgae and marine plants. Eliminating dead spots and stabilizing your pH at 8.2-8.4 can therefore help tip the balance back in the favor of macros and coralline algae, and help prevent problems with nuisance algae.

    One simple measure that can thus make a big difference is to try positioning one or more small powerheads so that they increase the circulation in the area where the black slime tends to grow. Better water movement and higher oxygen levels will naturally tend to minimize the growth of slime algae and hair algae in these problem areas.

    If you can cut down on your excess nutrient levels (especially nitrates and phosphates), maintain good water quality with the proper pH and alkalinity levels, physically remove as much of the black slime as possible and increase the circulation in the areas where it tends to form, you should eventually be able to eliminate it from your aquarium. But it can be a long, hard struggle once nuisance algae becomes well established in a tank and gets out of control.

    I’m glad to hear your remaining seahorses are doing better. Let me know if the measures we been discussing are effective or not. If they don’t make a dent in the problem soon, or your seahorses begin to develop symptoms of a problem, let me know right away and there are one or two emergency measures we can try to address this problem as a last resort.

    Best of luck eradicating that black slime, Kris!

    Pete Giwojna


    Thanks again…… I’ll keep working on it!!!!!!!!!!!


    Dear Pete,
    Ok, I’m sorry, I am really frustrated with my tank. I have done everything we had talked about and just when I think things are getting better…. the next day the entire floor of my tank it covered with the black stuff. It is now over all the coral and the plants.

    I have, several times, tried to scoop up as much of the slimey stuff as possible and it seems to help for a day or so, but the seahorses’ breathing seems compromised for several hours after stirring things up.

    My pH level was up to 8.1 as of this week end and the water is still showing 0 for NO2/NO3, NH3 and Phosphates.

    Would it be better to start allover again? Could I start with the "Natural Seawater" from the fish store? Does this have the normal bacteria levels in it, or would I have to cycle for several weeks all over again?
    One reason I am so concerned is that there was actually some algae growing on the back of one of the horses and I am now getting concerned for their welfare.

    As usual, I appreciate your help.

    Pete Giwojna

    Dear Kris:

    I can certainly understand your frustration with this problem. It must feel like you’re just banging your head against the wall and getting nowhere for all your efforts.

    If you wanted to start over, in order to do so and make sure you were getting rid of the slime algae or cyanobacteria in that aquarium for sure, you would pretty much have to break down the tank, sterilize everything, and then start over from scratch using RO/DI water or natural seawater to fill the tank initially. Of course, if you did that, you would need to cycle the tank again in order to establish the biological filtration, and it sounds like that’s something you would like to avoid.

    Before you resort to such drastic measures and start over with that tank again, there is one other measure you might consider as a last resort. There is a product called Chemi-Clean which is designed specifically to get rid of Cyanobacteria and slime algae in the aquarium. It is not an antibiotic and it is safe to use in reef tanks; it is said to be safe for corals, invertebrates and fishes in general.

    However, I hesitate to suggest this product to seahorse keepers except as a last resort. Chemi-Clean evidently acts by oxidizing the organic "sludge and settlements" that accumulate in aquaria, in a process which apparently consumes oxygen from the water in much the same way as formalin does. That is why the online instructions specify that you add an airstone, preferably one with a wooden air diffuser, to provide efficient aeration and oxygenation of the aquarium when you use the product.

    You must turn off your protein skimmer to use this product, which in itself reduces the aeration and oxygenation in the aquarium, and when this is combined with the oxidizing action of the Chemi Clean, which further reduces the dissolved oxygen level in the aquarium, it can create a dangerous condition for your seahorses due to the risk of asphyxiation. Seahorse setups in particular are susceptible to such problems because hobbyists are so conscious of their seahorses’ limited swimming ability that they tend to leave their aquariums undercirculated. Poor circulation and inadequate surface agitation can lead to inefficient oxygenation and insufficient offgassing of carbon dioxide.

    Seahorses are more vulnerable to low O2/high CO2 levels than most fishes because of their primitive gills. Unlike most teleost (bony) fishes, which have their gills arranged in sheaves like the pages of a book, seahorses have rudimentary gill arches with small powder-puff type gill filaments. Their gills are described as "tufted" because they appear to be hemispherical clumps of tissue on stems. Their unique, lobed gill filaments (lophobranchs) are arranged in grape-like clusters and have fewer lamellae than other teleost fishes, making them a little less efficient.

    I know one seahorse keeper who lost her seahorses overnight after using this product the day before. Chemi-Clean is not directly harmful to seahorses, but in her case, all four of her seahorses apparently asphyxiated overnight do to the decreased oxygen levels The Chemi-Clean causes when it’s working. That’s the reason I am reluctant to mention this product to seahorse keepers.

    However, in your case, I think it may be worth a try, Kris, since your only alternative at this point seems to be to tear down the aquarium and start over from scratch. It is designed to kill red-slime algae (Cyanobacteria) in particular, and I’m not sure if it will be as effective against the black slime algae you and battling, but I think it’s likely that your black slime is also a form of cyanobacteria, and if so, the Chemi-Clean may well eradicate it.

    If you want to try it, Kris, I would first relocate your seahorses to your hospital tank just to be extra safe. Then I would remove as much of the black slime as you could, add an airstone and a small powerhead to your aquarium to increase the surface agitation and promote efficient oxygenation and gas exchange at the air/water interface, and proceed to use the ChemiClean exactly according to instructions.

    Your seahorses should be just fine in your hospital tank for a couple of days or so while you are administering the ChemiClean and then performing a large water change afterwards. If you don’t have a hospital tank set up right now, you can use a large plastic bucket instead. In a pinch, a clean 5-gallon plastic bucket (new and unused, NOT an old scrub bucket!) can serve as a makeshift hospital tank. It should be aerated and equipped with hitching posts and perhaps a heater, but nothing else. This makes a useful substitute when the Quarantine Tank is occupied or in use and a seahorse needs treatment.

    After you use the ChemiClean according to instructions and have performed the requisite water change, reinstalled fresh activated carbon, and started your protein skimmer operating again, you can safely return the seahorses to your main tank and hopefully the black slime will never return. Please read all of the information at the following web site before you make a decision on whether or not to use the ChemiClean, Kris:

    Click here: Reef Show – CYANO BACTERIA: red-slime algae? Cause and Relief

    You mentioned that one of the reasons you are considering breaking down your tank and starting over was because one of your seahorses had algae growing on its back and you are concerned about its welfare. That’s perfectly normal and nothing to worry about, Kris. Seahorses in the wild actually encourage algae to grow on their armor-plated bodies in order to enhance their natural camouflage. So you shouldn’t be concerned that the algae growing on your seahorses harmful or try to brush it off or scrub it away.

    I always caution seahorse keepers against trying to physically remove such a coating of algae. Although the algal growth can be unsightly, it is part of the seahorse’s natural camouflage; it can certainly be brushed away, but doing so risks removing the protective slim coat along with the algae which can have harmful consequences. Allow me to explain a little more about the seahorse’s skin and mucosa and the important purpose they serve:

    We are all well aware that seahorses can change color to blend into their backgrounds, and that Hippocampus is capable of growing or shedding dermal cirri, which are long filaments and branching extensions of its skin, as called for in order to match its environment. To complete its disguise, the seahorse allows algae, bryozoans and other encrusting organisms to grow on its body, thereby rendering it all but invisible in its natural habitat. In fact, its skin contains polysaccharides which are believed to encourage algal growth, thereby helping it disappear into its surroundings. This vanishing act is so convincing that, even when they are collected by hand seining, seahorses often go undetected amidst the plant matter that accumulates in the net. Unless the collector is really diligent, he will lose a large proportion of his catch simply because many specimens will be overlooked and thrown back with the debris. In short, it’s perfectly normal for algae to grow on seahorses.

    The seahorse’s pliant skin or integument is of course its first line of defense against disease. It contains mucus glands, and the slime covering the skin acts as a barrier to ectoparasites and infection. The protective slime can contain antibodies and antibacterial substances, and excessive mucus production is often the first sign of an infection or parasite problem. On the other hand, healthy seahorses often have small bright dots on their heads and torsos, which are actually mucus deposits. These beads of mucus glisten like little diamonds and are a sign of vibrant good health. When handling a seahorse, it’s important to wet your hands first in order to avoid removing too much of the protective slime coat.

    Marine fish are always in danger of dehydration because the seawater they live in is saltier than their blood and internal body fluids. As a result, they are constantly losing water by diffusion (osmosis) through their gills and the surface of their skin, as well as in their urine. The mucus layer acts as a barrier against this, waterproofing the skin and reducing the amount of water that can diffuse across its surface.

    So, all things considered, it’s best just to ignore any algae that happens to grow on your seahorses. Removing it means removing the slime coat and mucous barrier as well, leaving the seahorse susceptible to infection and dehydration. It will secrete more mucous and repair its slime coat over the next day or two, but it will be vulnerable in the meantime.

    In short, Kris, the algae growth on your seahorse is normal and not at all harmful, which is another reason I thought you might want to try a product like ChemiClean before you tear down the whole aquarium and start over from scratch.

    Best of luck eradicating the black slime from your aquarium, Kris! Here’s hoping it’s nothing but a bad memory very soon.

    Pete Giwojna


    Hi Pete,

    By the time I got your last reply my tank looked like some alien swampland. The coral was all covered in black goo………. the plants were enveloped in the slime…. I couldn’t keep up. Honestly, is this the worst thing I have ever seen in a salt tank. I would clean it in the morning before going to work…. and by the time I got home it was worse than before.

    After hearing from you… I put the horses in a five gallon tank and went to work. Two day ago I was finally able to locate the chemiclean and things are looking much brighter!!! The slime has stopped growing and seems to be dying off………….. The horses are doing well in their "alternate" tank for now.

    My question is this.. How long do I need to keep the seahorses out of their tank?

    Thanks again for all your help. I am definately on the upswing here!!!!


    Pete Giwojna

    Dear Eric:

    It’s a relief to hear that you’re finally making some progress against the black slime algae. If it is dying off after treatment with the ChemiClean, then it is indeed a form of Cyanobacteria and you should be on the right track now.

    You must avoid running your protein skimmer or using chemical filtration for 24 hours after treatment with ChemiClean, at which time you need to perform a major water change (at least 20%). I have never treated a seahorse tank with ChemiClean, but I should think that after you perform the requisite water change and adjust your protein skimmer so it’s working efficiently again — and above all make sure your oxygen levels are back to normal — it should be safe to return the seahorses to the main tank. As an added precaution, you should also doublecheck all of your aquarium parameters (ammonia, nitrite, nitrate, pH, specific gravity, and especially the dissolved oxygen levels), but assuming they all check out, your seahorses can go back anytime thereafter.

    If subsequent treatments with ChemiClean are necessary to eradicate the black slime algae altogether, which could be the case with an aquarium that was as badly overrun with the stuff as yours was, be sure to observe all of the same precautions when you redose the tank. Once you have gotten the black slime under control again chemically, those preventative measures for nuisance algae and good maintenance practices we have been discussing all along should hopefully keep it from reappearing again.

    Best of luck beating that black slime algae problem, Eric!

    Pete Giwojna


    Hey Pete!

    Just a quick note to let you know that I am "Slime-less" Finally!!
    I followed all your advice right down to the Chemiclean. It took three applications, but its all gone. I thought I might lose one of my seahorses, as he was lying on his side with his tail all wrapped up around him. They were all still in the 5 gal. tank and when I saw him like that, I decided it was time to go back into to big tank. 30 minutes after putting him in, he was swimming and eating and all is fine.

    Again, thank you so much for all your advice!!

    Pete Giwojna

    Dear Kris:

    You’re very welcome! Thank you for the update — that’s most welcome news! I’m very happy to hear that you were finally able to eradicate the black slime algae that had taken over your tank, and that the rest of your seahorses whether the siege none the worse for wear. Nuisance algae can be very difficult to get rid of once it gets out of control, and I know how long and hard you have been battling this problem, Kris.

    If you can keep the phosphates and nitrates and other nutrients in the aquarium low, and observe the other preventative measures we have been discussing, the cyanobacteria should not return and your problems with slime algae should be over.

    Best of luck with your seahorse setup, Kris!

    Happy Trails!
    Pete Giwojna

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