Chapter III. Cyanobacteria control by increasing circulation

Whenever evil befalls us, we ought to ask ourselves, after the first suffering, how we can turn it into good. So shall we take occasion, from one bitter root, to raise perhaps many flowers. 

Leigh Hunt (1784 - 1859) 

So many people have problems with cyano over the years, and have asked for advice on fish forums, that the forums have generally amalgamated the discussions into FAQs or sticky's. While writing this blog I once again searched for such advice and the front page of google returned me to the same FAQs that I had read back in Jan 2011. I think it would be fair to say that the main causes of cyano problems are generally listed as.

• excess nutrients (nitrate (NO3) and phosphate (PO4) mainly) due to insufficient water changes, poor tank hygiene, overfeeding and/or overstocking.
• excess light/direct sunlight (although some claim insufficient light/wrong spectrum of light).
• insufficient circulation, cyano is said to favor stagnant conditions or even oxygen depletion.

You'll notice that the first point is the same as the suggested cause of green water which was easily solved by increasing the frequency of water changes. I guessed overstocking could have been an issue as at the time I had 21 fish. But according to aqadvisor.com, with the small species I had, 21 fish = 92% stocking. The tank didn't look overstocked to me. As for overfeeding, I have yet to see a piece of food make it to the bottom of the tank uneaten, so it's not that there was food rotting on the substrate. I never fed more than was eaten in two minutes but it was something to bear in mind.  

As for light, as I said before, I was pretty sure my set up was 'low light' due to the plants I was able to grow. But I did notice that the tank gets 1-2 hours of direct sunlight/day. I set the timer so the lights turned off for two hours in the middle of the day, which I remember reading on a forum had cured someones cyano problem. So the tank was getting 10 hrs artificial light and whatever the pale Scottish Sun could provide. Insufficient light didn't seem likely as I had enough light for plants to grow. Poor spectrum also seemed dubious as at the time the bulb I was using was only five months old. It also struck me that the most enthusiastic proponents of the idea that the deterioration of spectra from aging light-bulbs cause algal problems were light-bulb manufacturers. 

Circulation, this really caught my imagination. I had under-gravel filtration at the time, powered by a rising column of bubbles from an air-stone, but flow rates were probably low and as far as I knew there might have been 'dead spots' in the tank. I decided to increase water changes and increase circulation. I went back to weekly changes and in week 26 installed a power-head. The power-head made a big difference to the tank, all the plants were swaying and the fish started having to swim harder, in fact the X-rays started what looked to me like spawning.  I also became an expert at removing cyano. The best way I found was to siphon it off with the water. I attached a toothbrush to the end of my siphoning tube and found I could very efficiently remove it from the tank walls etc. and even Ellodea strands but not so well from the Amazon Swords or Java Moss.  I was still vacuuming the gravel weekly. The following photo is a still from a video taken 25-1-11 week 27.

This was shot two days after a 20 liter (37%) water change. I can clearly see the cyano growing up those Ellodea strands and the moss balls are tufty as they've been siphoned. I see I've planted Lilaeopsis in the foreground because the Java Moss had to go out, riddled with cyano it was. I then really upped the water changes. I was alternating 10-20 liter water changes every two to three days but the cyano just kept coming back. Not only that, it kept coming back more aggressively each time.  It would appear in new places and then once it had, removing it just made it come back quicker. By week 30 it became clear that increasing tank circulation had not had the desired effect. Looking back now it makes sense. It hadn't first appeared in a corner or under a rock but mid water. Why would circulation have been the cause?  It grew nicely on the power-head exhaust nozzle which must be the most circulated part of the tank. Something else was the cause and I decided to use science as my weapon.