Bob replies...

Hi Drew,

Extremely good questions, however, a few misconceptions.

Cyanobacteria/slime algae begins as a 'biofilm' which is nothing more than a very thin film or grouping of microorganisms that have found a home in a suitable neighborhood. Neighborhood preferences are where the current is somewhat slow, an adequate food supply exists, and where there is a preferred light spectrum. It can form on any solid matter that remains in contact with water, even living tissue.

The required nutrients are phosphate, nitrogen (as nitrate, nitrite, and/or ammonium). When the neighborhood is right, these films grow larger and/or hair algae spores find comfortable places to put down a mat-like growth and begin their plant-like structure (hair algae).

Since 'nitrogen' is probably the primary nutrient for getting these pest growths started, closed systems are the perfect place! Nitrogen is almost always above that found in the wild. Phosphate is also above that found in the wild, and the more foods that enter the water, the more phosphate, as foodstuff and possibly the tap water used for evaporation makeup and water changes are the two main sources of the compound in our aquaria.

Nitrogen (basic foodstuff) is normally high near the substrate-bulk water interface where mineralization and nitrification is occurring (yet maybe not too high in the bulk water). Equipment such as trickle filters and fluid bed filters discharge nitrate into the bulk water, not helping the situation. If small adjacent supplies of phosphate (energy) are also available, it's almost the perfect place to call home. Since these are autotrophs, add to this environment a poor quality spectrum (red wavelength) and somewhat poor water movement,, and the neighborhood becomes the best possible place to call home!

Once started these existing forms of cyanobacteria (slime and hair algae) would be unaffected by additional nitrogen additions to the bulk water, except to possibly create new areas of growth. Nor would water changes provide any long-term solution to a nitrate problem. Water changes are a nothing more than a very temporary treatment as any nitrate inside the bed or rock will simply flow back out into the bulk water within a day or two and you're back to square one. It's necessary to get to the roof cause. That would be doing what is necessary to reduce/rid the cause of any nitrogen and phosphate levels in the bulk water, and physically remove unwanted growths. And to continue to remove these growths as often as necessary while improving the quality of the bulk water and accomplishing sensible sandbed maintenance.

As for calcium precipitated phosphate, such as precipitated with Kalkwasser, it does not generally reenter the bulk water. Generally is the key word! That's because in the bulk water area the compound is quite stable since it can very easily maintain its electrical 'charge' balance. In other words, the phosphate compound is four oxygen atoms and one phosphorus atom (PO4) all held very firmly together by their electrical charges. If the calcium phosphate compound were to somehow be transported into an anaerobic area, bacteria would attack the compound for its oxygen elements, thereby releasing the phosphorus element. Phosphorus by itself is not an algae nutrient in the sense as is phosphate/nitrogen (ammonium, nitrite, and nitrate). Yes, 'phosphorus' is necessary for the microbes to carry out their metabolism processes, but its not a direct player as an algae nutrient. However, phosphate, a byproduct of that metabolism, is!

However, there's another 'possibility' when it comes to cyanobacteria. Once cyanobacteria mats/biofilms/hair algae begin, the area under the mat is subjected to reduced oxygen levels. If the calcium phosphate compound is under the mat area, the bound phosphate could be liberated due to the bacteria seeking the oxygen elements. To what degree has not been determined to my knowledge, nor exactly its value to the structure of the mass. However, it certainly must help in the initial growth stage. And, it should be understood that the continued growth of the mat or hair-like cyanobacteria becomes independent of nutrients in the bulk water because its mostly fed by what's being produced in and just under its mat area. In fact, at this stage, the reduction of light is ineffective. And, as a last comment, phosphate, as orthophosphate might be released to the bulk water by tunneling infauna while its being oxidized, but even that is fairly rare in closed systems.

In freshwater aquariums its possible to use a small amount of brown sugar or unprocessed honey monthly to feed the aerobic cultures that use the ammonia as fuel, thereby mostly doing away with nuisance algae. As for how much, one teaspoon in a 100 gallon aquarium would suffice. Table sugar does not have the same carbohydrate value because of bleaching, as do these unprocessed sugars.

As for the use of a phosphate sponge, I do not agree with those that say its possible to absorb the phosphate already bound to calcium. That phosphate would/could only be released by acidic conditions or reduction by microbial processes. However, 'iron' based products are extremely useful in removing it from bulk water. There are three pad brands that I know of, and a growing number of excellent iron-based powdery products. (For those reading this, contact me for brand names and recommendations) Unless green is your favorite color, one of these iron-based products should be used from startup.

There has also been some controversy over the safety of aluminum-based phosphate removing products where some soft corals are concerned, i.e., Sarcophyton sp. I have been recently informed that at only a pH of 8.5 and above does aluminum-based products possibly become harmful to these type soft corals. I would like to see more data about this possibility and if anyone reading this has further data, please contact me.

Hope this answer's your questions.

Bob