Re:Black Slime

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!

Respectfully,
Pete Giwojna