Re:Black Slime

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

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