06-15-2012, 06:19 PM
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Originally Posted by Nemo the Clownfish
I've got a sort of question related to this discussion. For purpses of this question, let's assume that at night in a low tech tank with the hang-on-back filter off less surface agitation would keep CO2 longer in the water more at night. I assume that photosynthesis during the day would be able to proceed longer without surface agitation during the night.
I have a hang-on-back filter which creates plenty of surface action. I would like to turn off the HOB at night. I figure that since the fish are less active at night and use less oxygen they'll be alright. Will the results be significant enough to warrant the change? Will the stagnancy at night work negatively?
Appreciate any analysis.
You should never turn off the main filter, at any time. Bacteria in the filter need oxygen, and stopping the water flow for more than an hour or two (as when doing a water change) will suffocate the anaerobic bacteria. Depending upon the fish in the tank, this could harm them too, in a couple of ways.
Filtration and water flow are two very different things, though they obviously are connected since both are normally due to the filter.
In a balanced natural-method planted tank, there will never be any shortage of oxygen or excess of CO2 that will cause any issue for fish.
CO2 definitely builds up during darkness, otherwise the natural or low-tech method wouldn't work at all. In most natural planted tanks, the CO2 will basically be used up during the light period, so it has to be replenished during darkness. And keeping surface disturbance minimal will prevent it from being driven out of the water faster.