bristle nose pleco question
That’s true IF the tank has a filter on it. Once my planted tanks get established, I don’t have filters on them. So oxygen levels can and do drop at night. That’s why I feel properly balancing the fish and plants is so important. 
When I say I do low tech, I do mean low tech. Established tanks have heaters (sometimes) and lights, and that’s about it.
So I never assume that someone else’s tanks have filters, or that those filters are working properly or causing sufficient surface turbulence to affect oxygen exchange between water and air.
Dawn T
>>> A planted tank does not experience low oxygen levels at night due to CO2 >>> levels as the two gasses do not interfere with eachother’s concentration >>> (one does not displace the other). A tank, planted or not, should have >>> sufficient turbulence/movement at the surface (from your filter’s >>> return) to assure a sufficient rate of gas exchange. This is key in >>> setting up any aquarium, HOB filters automatically cause such turbulence >>> as they drop the water back into the tank from above the surface, >>> however a return from a canister filter could be positioned too far >>> below the surface to cause problems. Most tanks in such a condition also >>> tend ot build up an organic film over the surface due to insufficient >>> movement. >>> >>> Giancarlo Podio, LMD
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