The wood has started growing a layer of what could be either bacteria or a fungus, which is apparently common in aquariums with a higher pH. I have seen this happen on a re-used piece of mopani wood before: it usually stops growing the fluff after a while. Without analysing a sample of the fluff, it would be impossible to find out if it really is a bacteria or a fungus. I took the wood out of the aquarium and washed it off. The fluff feels slimy to the touch, but is harmless.
This morning’s test results were:
- ammonia: 1 ppm
- nitrite: over 5 ppm
- nitrate: 5-10 ppm
I misread nitrite in yesterday’s reading, it was closer to 3-4 ppm.
I have also noticed that the soft plastic inside the aquarium has started growing a white, fluffy fungus on it. This happens to most new plastics, nowadays, and is nothing to worry about. The photo above shows the fungus on the spray bar end cap, where it is at its worst. The photo to the right shows the power cord covered in a pale, milky membrane. The fungus is soft and slimy to the touch, readily flaking off when disturbed. One can either remove it manually, or wait for it to flake off on its own and be picked up by the filter sponge.