After reading a series of message exchanges dealing with micro-algae the other day (the messages were posted on several mailing lists including ours), I began to think a little more about those sudden and unexplained algae outbreaks that hobbyists so frequently report.The hobbyists recount the occurrence of such algal outbreaks even when water testing seems to indicate that all water chemistry quality parameters (especially phosphates) are extremely low (for instance PO4 is around 0.03 ppm.), and within the recommended ranges a set of circumstances where micro-algae should not grow. This also means that nitrates and silicates are low.
Such low phosphate and other nutrient concentrations, and the fact that other water quality parameters are completely in line with generally recommended safe levels, should "not" give rise to the appearance of micro-algae "at all", yet hobbyists report that they nevertheless happen and often occur suddenly, at the most unexpected time.
This is happening to both experienced and beginning hobbyists alike. Everybody, even the experts, are stumped when this occurrence befalls them.
This being the case, why do these micro-algae suddenly appear even though aquarium conditions and water quality do not account for such growth at all? Here is an explanation which can account for these outbreaks.
It has been postulated, and proven, that the long term use of Kalkwasser precipitates phosphates out of the water (which Kalkwasser really does by the way) and that these phosphate based compounds settle "on" and "in" the rock (live rock) in the aquarium, as well as "in" and "on" the substrate that may be present in the aquarium.
This is the case too, of course if your tank contains Live Sand. In fact, Live Sand makes a real good settlement area for phosphate based compounds (all of them are complex compounds, a part of which is phosphate).
Since these compounds are "not" soluble at high pH levels they are really not a cause for concern as, in their insoluble state, they are not available as nutrients for up-take by micro-algae and its growth. As long as they remain in a high pH area, they will not give rise to algal growth because the phosphate they contain is "bound" and thus not available to algae or for algae to grow.
Over time they simply accumulate more and more in the tank as "insoluble matter" which can, by the way, be siphoned out from time to time (not weekly, but monthly or every two months perhaps). As a matter of course anything that settles on the rock and on the sand should be siphoned out. Not only does this keep the water cleaner but it will prevent what I am about to explain and postulate as the cause for these sudden unexplained outbreaks of undesirable green algae.
Insoluble matter is of no concern, since it cannot affect tank conditions. In its insoluble state it is also inert and does not react in any way with the water in the aquarium. In this state it certainly cannot provide nutrients for micro-algae to grow profusely as is reported by hobbyists.
The reason for the growth of algae lies elsewhere. As we shall see though, it is very much connected with these "settled" phosphate containing compounds.
Apparently situations can and may, however, occur whereby "certain" areas of the tank actually exhibit a different pH level than the one measured in the main water body of the aquarium.
By different I mean in this instance: lower and sometimes quite a bit lower than the aquarium's pH level. We are not aware of this because we do not measure the pH in those areas. We only measure the pH of the aquarium water itself.
Where would this occur and why? Can this, in fact, occur at all? The answer is "yes" in all cases, as demonstrated by empirical evidence that such micro-algae outbreaks do occur (the reports by hobbyists and testing conducted on aquariums that were aged and where kalkwasser had been used). Mind you, the use of KW is not the only reason that phosphate may precipitate out of the water. Other chemical reactions that occur in the tank can make this happen as well.
These outbreaks may not be the norm, but they happen frequently enough to be a cause or reason for concern, hence this document that explains why this may happen and what can be done to prevent it from happening.
Many hobbyists who call me have noted that such sudden growths have happened to them even though they have adhered to superior aquarium maintenance, husbandry techniques and practices. Their appearance is therefore not due to lack of maintenance or neglect of the tank and the water chemistry.
In view of these findings do we have to accept these unexpected algae growths and outbreaks as a fact of life, something that can happen to any hobbyist at any given time? Or, is there some sort of reason or explanation for this growth?
Fortunately, the explanation is a lot simpler than one actually thinks. The remedies are not difficult to implement either, as we shall see, and the solution is not complicated. These outbreaks can be prevented.
Some very good points were made in some of the messages I read. The germane ones really made a lot of sense to me and can indeed well be the explanation for these sudden appearances of micro-algae, when only days before the aquarium was completely devoid of it, clean and free of algae and diatoms.
The conditions and chemical reactions that in all likelihood lead to those outbreaks are really quite simple when one thinks about it for a while, and they make a lot of sense from a chemistry and nutrient availability standpoint too.
Here is what I postulate and surmise:
Phosphates that are "bound" in an insoluble form and are, therefore, not available to algae "can" and "will" go into solution because of pH fluctuations in certain areas of the aquarium, areas where a much lower pH exists or develops, than the actual pH of the aquarium itself.
These pH drops in certain areas are due to nothing more than basic chemistry principles, but principles we all may have overlooked up to now. You may recall, though, that in my books I have often stressed that live and other rocks should be regularly cleaned off and that any precipitates should be removed.
Little did I know at that time that I had hit more than one touchy area.
My recommendations had to do mostly with removing organic material that may otherwise decompose. It turns out now that these regular cleanings have an additional benefit: removing insoluble phosphate based compounds, thus preventing them from fitting into the scenario described here.
When the pH drops in those areas of the aquarium, these insoluble compounds break up. Because they are in low pH areas the compounds dissociate, resulting in ortho-phosphate that goes back into solution, giving rise to the sudden appearance of micro-algae growth, a growth that was totally "unexpected" and "unpredictable" given the tank's water quality conditions.
As indicated, this falling pH syndrome occurs mainly in two types of areas in the aquarium:
Pollutants may build up in those areas and create conditions favorable for the pH to drop quite a bit (even though the drop is very localized and does not spread to the rest of the aquarium).
- in the substrate (whatever its type) and
- in crevices in the live and other rock, present in the tank.
These localized drops in the pH level in the areas mentioned above, dissolves the phosphate based compounds that are present there, these phosphate based compounds that were previously inert and now no longer are.
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