Forgot to switch the filter back on after feeding
I briefly switch off my filter (canister filter, 12 liters volume) for feeding my discus, i.e. I only close the outlet valve. Has been working excellently all the time!
However, the last time I fed them in the evening (they get something up to seven times a day) I actually forgot to open the filter back again. When I came home from work the next day, I hardly could believe what I saw. The tank was completely milky! Luckily though, I do aerate the tank as well! I immediately carried out a large partial water change...
that was good and correct...
... and cleaned the filter.
... that, however, was probably not necessary.
Today, the water is crystal clear again, and the fish (discus, catfish, neon tetras and butterfly cichlids were obviously not affected. Now my question is: What caused this "milky water cloudiness"? Bacteria, protein or precipitated iron (Fe approx. 0.7 mg/l), or even something else?
These were rather certainly bacteria and other protein metabolizing micro organisms (so-called infusoria) that were not drawn into the filter (where the organic matter would have been processed normally) and multiplied correspondingly - one might call it 'moving the filter processes into open water'. Trouble may occur if the oxygen consumption becomes so severe that fish suffer from shortness of breath or even suffocate in the worst case. Breaking down organic waste requires much oxygen, and oxygen uptake from the atmosphere in standing water is much lower than in appropriately agitated water.
Dr. Bodo Schnell