Chapter 17. Maybe it was all a coincidence.

It's four weeks on from Chapter XV and it is becoming clear that heating the AW to 70 C before using it for a water change did not result in an increase in cyanobacteria (possibly Jaagenima see Chapter XVI). Not only that, but the same process of gradual die-back has continued. I have made a slideshow covering the period week 114 through 124 focussing on an Amazon Sword plant. It's available on youtube.

The final two stills cover the period after heating the AW, the tank looks better than ever. For the last two changes (week 125-126) I have been using ordinary tap water (it's good not having the hassle of running a second air-stone and heater), and so far no sign of a return either. There's still cyano in there of course.

Week 125.  Cyanobacteria hunting

Waiting, patiently, the only remaining species 1 mat is on the plastic filter housing (top left). There's a little species 1 in amongst the Java Moss as well (it's obvious if your eye's in) and what looks to me like a mixed (species 1/2) fine mat on the bogwood.

Week 125.  Fix bayonets.

The fact that heating the AW didn't result in any increase in cyano might suggest (if you believe what you read in Chapter XIII) that it wasn't the microbial community in the AW that affected the cyano. But the fact that going back to tap water hasn't caused a recurrence means that it is a formal possibility that the whole thing was a coincidence. I don't think I can conclude anything because the fact is my aquarium has fundamentally changed.

1. The pH has lowered from 7.6+ to around 7.2. 
2. Nitrates now accumulate between water changes.
3. The plants are growing.
4. There is a lot less cyanobacteria.

1. As for the pH dropping, I think I made a big mistake in Chapter XII. I measured a drop in tank pH in week 115 it's true but, looking back at the calender I write all my tank notes on, I see that I first recorded a drop in tank pH in week 111, one week before the first AW change. It seems that this slipped my mind when I wrote Chapter XII. So the statement " It seems maturing my tap water for a week results in a lowering of its pH. And that by using it for water changes I have lowered the pH of my tank" was wrong. I don't know why the pH of my tank dropped and I don't know when because the closest pH reading I can find is 7.6+ in week 37. I gave up measuring the pH back then because it was always the same. Maybe the death of the Cardinal in week 115 suggests the pH drop had been recent. Or maybe the cardinal just died.

2. As I said in Chapter VII, at the height of my cyano problem levels of nitrate dropped between water changes even though I was adding KNO3. At the time (week 50) I gave up testing for nitrate because I had decided that nitrates and phosphates didn't have any effect on my cyano problem. I started testing again in week 115. Levels were close to zero and remained so until week 117, since then they have tended to increase. These last few weeks they have been around 1-2.5ppm. The simplest explanation of this would be that the cyano was using up a lot of nitrate, but that might not be the only reason. 

3. As you can see from the slideshow, the cyano die-off has had a dramatic effect on the plants. They're all growing, but the Amazon Swords are growing well. The mats that covered them were on both sides of the leaves so I'm amazed they survived. Amazon Swords are the ultimate low light plant.

4. I don't bother cleaning the remaining cyanobacteria any longer. Live and let live I say.

Whatever the cause, the change has been dramatic. It's like a totally new aquarium with a different balance of organisms, a new ecosystem if you will. One of the most dramatic changes is the amount of algae. I used to get some green spot algae on the tank walls (especially the back wall). As you can see from the slideshow, the green spot turned orange, then brown and was easily scraped off with a scouring pad on a stick. I haven't seen any green hair algae since I stopped adding nutrients. And yet I'm testing positive for nitrates, so by definition there must be an excess in my aquarium. It seems that the changes in my aquarium that disadvantage cyanobacteria also disadvantage green algae. Of course all this has made my life a lot easier. Cleaning the tank takes about 5 minutes and I can do a water change in 45 minutes. It used to take hours.

However, intellectually this is most dissatisfying. I have no idea what caused my cyanobacteria outbreak, and I am uncertain what solved it. The whole point of starting this blog was to say something sensible about the causes of cyanobacteria problems and to provide some advice that was based on reason. All that is left to me is to speculate.

It's possible it was all a coincidence, but it's also possible that using AW for ten weeks (weeks 112-122) set in motion a chain of events that could not be reversed by going back to tap water. I imagine it's possible that once the ecology of an aquarium changes, once new species become established, the previously dominant species can never naturally take over. Maybe if I'd gone back to tap water after five weeks I would have seen a recurrence. But I got spooked by the Cardinals demise, I didn't realise the pH of my tank had already dropped. There is a way to test my theory. If I have learn't anything about the causes of cyanobacteria in my fish tank, I should be able to trigger an outbreak by dosing with antibiotics. This should convert the tank to a state that previously has favoured the dominance of cyanobacteria after using tap water for changes. I would be very interested to know the effect that would have on tank pH. If the cyano returned I could then test if using heated AW could reduce the cyano, and if it didn't, I would be able to repeat the observation that AW did reduce cyano. It's Christmas eve tomorrow and I am in no mood to start a cyanobacteria outbreak, but in the new year, if I don't see any return after 10 weeks of tap changes, I'll think about it.