Aquarium Slime: What is it & what to do about it?

That Pet Place


5/16/2018 9:55 am
"Slime algae" is a common problem with aquarists of all levels but getting rid of it can be tricky. The name "slime algae" is a misnomer. Because Cyanobacteria are photosynthetic and aquatic, they are often called "blue-green algae". In reality they are NOT algae, but something more in between algae and bacteria. Cyanobacteria are bacteria that manufacture their own food and live in colonies -- large enough for you to see them! It’s these colonies that cause trouble for aquarists. They are not necessarily blue-green but can be black, green, blue green, and the familiar dark red sheets covering many surfaces in an aquarium.

The first thing aquarists who find an unwanted colony of cyanobacteria in their aquarium want to know is how to get rid of it. Well, this is where it gets tricky. To eradicate the problem – the particular trigger for the cyano bloom must be identified and treated. Not every bloom is in response to the same trigger and while throwing a chemical at the problem will perhaps clear it up temporarily, it will come back, and it will be worse. (More on this later.)

As with all types of algae, any uncontrolled growth indicates an imbalanced system. An imbalance in one or both of two main triggers can set off a cyano bloom.

• DOC - Dissolved Organic Carbon is a food source of the bacterial side of the bacteria-algae. Sources of dissolved carbon include: fish slime, algae, bacteria, digested/uneaten food, metabolic waste, live food, some aquarium additives etc.

• Lighting - The food source for the algal side of the bacteria-algae is light. Light bulb spectra shift to red as they age, resulting more favorable conditions for photosynthesis to take place more vigorously.

Note: It is said that slime is caused from phosphates and silicates in the water. It’s true that these 2 elements will certainly grow algae of all sorts, but if removed will not reduce or remove a slime problem.

Okay - so what DOES remove the problem?

• Control your DOC. This is best done by frequent water changes, good water movement (power heads and closed system circulation) and (this is important!) a good protein skimmer. An undersized or ineffective protein skimmer, high waste loads, or a combination thereof will increase the dissolved carbon level. As a rule of thumb for skimmers; buy one that is rated for at least twice the size of your tank. It may take some adjusting but a properly functioning skimmer can remove ½ cup of thick organic scum from a tank a day.

• Use an RO/DI filtering system (Reverse Osmosis/Deionization) for water changes whenever possible. This eliminates adding DOC into your tank via tap water.

• Add more lighting or change your bulbs. Change bulbs at least once every 9 to 12 months, don’t wait till they burn out. To be more cost effective, you can stagger your replacements rather than replacing them all at once, but if the slime persists you may have to go all out and do full replacement.

• Watch what you feed. Feed once a day. If you wish to feed twice, simply split the amount in half – don’t feed twice as much food. If you feed grocery store bought seafood or are making your own foods, rinse all foods thoroughly as seafood sold for human consumption is treated with phosphates and preservatives to keep it fresher longer. (It’s true!) Avoid flake foods, these dissolve too fast – pellets and crisps are much better and more palatable.

• If you aquarium is freshwater, the above treatments still apply, but a protein skimmer is not used. Water circulation, frequent water changes, extra charcoal filtration and changing lights all will be effective controls.

Disclaimer: I am in no way saying that if you have a slime outbreak, that you are a bad aquarist and your water is swill. Even in the best kept tanks there are still cyanobacteria. You will, in fact, see outbreaks in systems which are free of phosphate and silicate; they also have new halides, actinics and great water flow. There is always another factor – vitamin supplements, liquid foods, and other additives can add the organics that can trigger a cyano explosion. Look for anything different you are doing and stop doing it.

Right – that covers the long term, not so easy fix. But for those who still want a quick fix, there are products that are available to help remedy the problem. BUT – if the underlying issue is not addressed, don’t say I didn’t warn you…..

• Cyano is a gram negative (thin cell membrane) bacteria, much like most bacteria in the aquatic environment. A dose of Erythromycin will knock out the colony of slime quite quickly. However, since the nitrifying bacteria you need in your tank are gram negative as well, they will be affected also, either being killed or severely damaged. This treatment is more advisable in freshwater aquaria, but only with careful attention paid to water quality while treating. Like all antibiotics, if dosed frequently the cyano will develop a resistance.

• Chemi-Clean by Boyd Enterprises and Red Slime Control by Blue Life are highly effective reef safe treatments for slime. These are non-antibiotic formulations and will do less damage to your biological filter. If used frequently however, there is still a chance of the cyano developing a resistance.

I hope this info is helpful in your endeavors to keep a slime free tank. For more and more thorough information, check out these links! Happy Fish keeping!