Red Slime Algae; Cyanobacteria Questions, Read Here First...

[rshimek]

Hi,

Red slime algae, "red" algae, cyanobacteria mats, etc., all refer to the growth of red photosynthetic bacteria (= cyanobacteria) in a reef system. As with growth of any other organism, such growth indicates proper conditions for their growth. Such algae are ubiquitous in marine systems, and are even common on natural reefs, so having them in a reef tank is not surprising. Their dominance in reef tanks, however, reflects a lack of - primarily - benthic (= bottom dwelling), detritus-feeding animals, or a sufficiently active biological filter, or an inefficient nutrient export system. Remember, whatever you add to a tank remains in the tank unless it is actively exported in some manner.

Consequently, these red algae are the main symptom of at least one - and generally more - larger problems. Illumination has nothing whatsoever to do with this, and chemical treatments won't cure it.

Basically, the tank has accumulated a large amount of soluble nutrients and the cyanobacteria "bloom" because of that. You need to do whatever it takes to bring the nutrient levels down and keep them down.

The basic solution must involve:

Water changes: frequent and large water changes, siphoning out as many of the algal mats as possible. Wait a day or so between changes to allow the algae to grow, so you have something to siphon out. When the algal growth slows so that you are waiting a week or more, you will be making headway.

Good biological filtration: You need to have the maximum production of nitrogen gas from the nitrate and ammonia sources in the tank. A well maintained and set up deep sand bed can do this, but so can some other sources.

Good export: You need good skimming - this removes nutrients that won't be turned into a gas (i. e. phosphates, sulfates, excessive amounts of trace elements). Additionally, use "biomass export" to remove nutrients. This involves growing other algae, typically macro algae such as Caulerpa or Chaetomorpha, or alternatively some soft coral or sponge that will also absorb some nutrients. As these organisms grow, harvest and remove them and the nutrients in them from the system.

Stop adding any trace elements: No animal needs them, but for algae they are fertilizer and they stimulate algal growth.

Regulation of bioload and feeding: You may need to reduce the bioload in the system and adjust feeding accordingly. Animals (all animals) produce ammonia and phosphates as waste products. So does the decomposition of foods. Without a good biological filter, these materials will fuel the algae. To this end, you may have to bring the bioload down to a reasonable (= low) level. Many tanks are overcrowded, and in these systems, it is essentially impossible to even "catch up" in the nutrient management race, let alone, win.

Animals that eat the algae are few, and are not too helpful. The nutrient they eat (with the exception of some that get converted to carbon dioxide and nitrogen by various metabolic pathways) never leaves the system and continues to fuel the algae.