No, sir, a short hypersaline bath or treatment with fenbendazole should not be harmful for coralline algae. However, it may have been set back a bit if you were too overzealous in your initial attempts to scrub it off your live rock after mistaking it for a colony of hydroids.
The attractive coralline algae can appear in a number of colors ranging from purplish to pinkish or even reddish, and it will grow and thrive on live rock and other surfaces in the aquarium providing the lighting is not too intense and you maintain the pH, calcium, and alkalinity in your marine aquarium at the proper levels. Unlike most other algae, coralline is a form of calcareous algae and it needs sufficient calcium in order to grow and prosper.
The most common causes of bleaching or death of the coralline algae are lighting that is too strong or a problem with the water chemistry (i.e., the pH, calcium levels, and/or total alkalinity of the aquarium water are out of whack). So the best thing you can do to encourage the growth of your coralline algae is to keep the light levels in the aquarium low and maintain optimal water quality, including the calcium levels and carbonate hardness/total alkalinity. Here is some information you may find helpful in that regard:
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 7.9 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
Seahorse keepers with fish-only systems need not be overly concerned about many of the parameters mentioned above, but if you keep alive corals and/or coralline algae in your aquarium, then you will find it helpful to monitor most of the above water quality parameters. Again, the pH, calcium levels, and alkalinity are the most important for assuring a good growth of coralline algae. And, you must keep your phosphate levels as low as possible (ideally at zero) both to avoid problems with nuisance algae and because high phosphates will inhibit the growth of coralline.
Once your aquarium has finished cycling, there are a couple of other things you can do to encourage our coralline algae to grow and spread. For example, there is a product called "Purple Up" by CaribSea that is designed to stimulate the growth of coralline algae. It’s a supplement that you add to the water in order to accelerate the growth of pink and purple coralline algae. It adds Ionic calcium and replenishes iodine, which the coralline algae needs for growth. Since it is not a plant fertilizer, it does not promote the growth of nuisance algae, but rather just stimulates better growth of the beautiful coralline algae.
You can also pick out one or two small (2-3 inch) pieces of live rock from your LFS that are heavily overgrown with coralline algae and position them in your life tank atop your live rock where the water flow is strongest. This will help disperse new coralline algae spores throughout your aquarium and promote the growth of new coralline colonies.
For more information on encouraging the growth of coralline algae, please review the following articles and discussions:
That’s weird about the salinity or specific gravity in your two aquariums being so different. If they are plumbed together so that the water can circulate freely from one to another, the water quality in both tanks should be virtually identical. How are the two tanks connected, sir?
If water is not exchanged between the two aquariums continuously, then you will need to monitor the water quality parameters in both tanks separately and adjust them accordingly.
Best of luck with your new seahorse setup, arcprolife. Here’s hoping that your diatom boom is soon a thing of the past and your coralline algae thrives and encrusts all of your live rock.