Chapter XIII. Theorise!

The results of the pH tests showed that I hadn't thought of all possible reasons why AW might reduce cyano numbers in Chapter XI. With this in mind I now think there are three possible reasons, but I would be interested in other opinions.

1. Ecological. The aging process results in the growth of a population of bacteria/unknown organisms (probably heterotrophic bacteria) in the AW who directly compete with the cyano for space and nutrients after being added to the tank.
2. Nutritional. During the aging process the AW is depleted in a factor (X) that promotes cyano growth. The mechanism could be biological (e.g. uptake by bacteria) or chemical (e.g. precipitation/chelation).
3. Chemical. The aging process results in a change in water chemistry so that it no longer favours the growth of cyano (e.g. pH).

They're all interlinked of course. A drop in pH could increase the rate X precipitates, X could be a factor which discourages the growth of bacteria Y, which compete with cyano etc.

Anyway, I thought of an experiment that might help eliminate pH as a possibility. I could add the minerals I bought before Arthurs intervention to my tap water and then age it. According to the manufacturer this would result in raising the carbonate hardness by 4 dKH, and the general hardness by 7dH. As a result the acidification of the AW should be prevented by the extra buffering compounds (bicarbonate (HCO3) mainly). I haven't tested my tap water for carbonate hardness, but I think the water here is soft. If it wasn't I wouldn't be seeing a drop in pH in the AW. Also, my unheated goldfish tank pH is 6.0 or below before a monthly water change and usually ~6.4 afterwards. This suggests that my water has very little buffering capacity. It has always surprised me that I never took a pH reading below 7.6 from my tropical tank before I started using AW. My plan was to switch to fresh tap water until the cyano came back (assuming it did), this should gradually cause a slight increase in tank pH (~7.0-7.6+) over a period of around three changes. Then if I used the modified AW, I might see a reduction in cyano with no decrease in pH. If not then it would suggest that pH was important. Unfortunately I can't risk it. A fish-keepers primary responsibility is to his or her fish. Also it would take weeks.

As an alternative I will try and eliminate 1. Ecological as a possibility. Of the three, it's the one I think most likely (I will explain why later). What I will do is age the water as usual but before using it, heat it to near boiling point for five minutes. This should kill 99% of bacteria etc. but I think leave the water essentially unchanged. If I measure no difference in pH before and after the heating I will add it to the tank. If i see an increase in cyano numbers in the tank it would suggest that the ecological composition of AW is its important quality in limiting cyano growth rather than it's chemical composition. This is a better experiment because I will hopefully be changing far fewer variables than the comprehensive change in water chemistry required for the pH experiment. One thing I will be doing different is probably adding a very large number of bacterial corpses.