Chapter 19. The rise of the Cyanobacteria.

Week 137

Week 139

So to re-cap. By week 137, 13 weeks after reverting to standard tap water changes, a uni-cellular cyanobacteria had largely covered the Amazon Sword plants and was growing in the Java Moss. There were also small patches of species 2, particularly in the Java and on the Moss ball. It is strange that the Elodea and Hygrophila  seem much less affected. But the cyanobacteria outbreak (if you can call it that) was mainly a plant problem. The gravel and tank walls were largely clear. Then in week 139 the brown colonial mats on the Amazon Sword plants started dying.

Week 141

Week 143

By week 141 they had died right back, this effect was tank wide. I don't know what caused this sudden population crash, or the gradual increase before it. But I may as well state that for the 15 previous weeks the levels of nitrate I measured varied between 0.2 and 1.0 ppm with no general trend I can see. No explanation then for the re-appearance of what I assume are unicellular cyanobacteria on the Amazon Sword, bog-wood and, importantly I think, the gravel (week 143 above). It's also growing on the glass. It is at this point that a cyanobacteria population becomes a problem, because anything that obscures the view or makes the gravel look dirty is an embarrassment.

Week 145

Week 146. 

In week 145 I forgot to photograph the tank before I had cleaned the tank walls. This is why they look clear, but you can see that there are species 2/brown mats on the gravel and the Hygrophila, in fact all the plants are now affected.  Notice how red the brown mats can be, it reminds me of the cyanobacteria seen in reeftanks. By week 146, species 2 was starting to dominate the tank. Nitrate levels had dropped to undetectable for weeks 144-146, but I see no reason to think this has caused the recent increase in cyanobacteria. It could just as easily be a consequence.

If you compare these pictures with the one at the beginning of the previous post, it's clear that cyanobacteria (of one sort or another) have increased dramatically over the last 20 weeks. It's the classic pattern, the more I syphon off, the more grows back. The traditional advice would be to increase the frequency of water changes, or maybe to add nitrate, but I know from experience that would be futile (see Chapter VII).

I would like to make two points about my new cyanobacteria infestation in comparison to the previous species 1 (Jaaginema?) in terms of aquarium maintenance. Firstly; the new species do not smell as strongly. The characteristic smell of cyanobacteria is apparently due to chemicals they produce, mainly geosmin and MIBs. They are said to give cyanobacteria an "earthy smell" but I prefer to think that soil smells of cyanobacteria. In all my reading about cyanobacteria identification and classification I have not seen smell mentioned as a criterea to define genera. Maybe it could be. What I can say is that species 1 (Jaaginema?) produces lots of geosmin/MIBs whereas species 2 (Lyngbya?) and 4 (Unicellular) do not.

Secondly; they are much less sticky (see video). During the first infection, it was very difficult to syphon a species 1 mat off a small plant and impossible to syphon it off the gravel. It would always hang on to enough gravel to weigh it down in the syphon tube. These new species come away nicely. So, the tank doesn't smell and it's easier to remove the new cyanobacteria, but it still gives the tank that primordial vibe. I prefer the verdant green spotless tank of week 126 so I will try and reduce the cyanobacteria in the same way as described in Chapter XI.