As I understand it:
Dissolved oxygen % is based on equilibrium with the atmosphere, which is 21% oxygen. Under normal circumstances (in other words, excepting temporary special conditions like rapid temperature changes), unless pure oxygen is being injected into a tank, good aeration (through surface turbulence created by filters, airstone, etc.) will balance dissolved oxygen with atmospheric oxygen, what's called 100% dissolved oxygen. So with good aeration and water quality, short of testing with DO test equipment, you can assume you're at or near 100%. 100% is within the range the studies I've seen say is optimal for fish growth (typically 80-120%).
The aquaculture experiments test for higher than 100% DO, which is possible because photosynthesis or direct oxygen injection can add dissolved oxygen to make it higher than atmospheric oxygen. Meanwhile, in most of our tanks, "aeration" is still exchanging gases with the atmosphere-- trending down toward 100% if you have plants adding 'extra' oxygen. I don't know this, but it seems reasonable that a planted tank with light, little, or no water flow could exceed 100% DO (daytime). Otherwise, I expect most of our tanks that have good aeration are at or near 100%. In other words, going beyond good aeration to add extra' aeration (in effect, exchanging more air with the atmosphere, still at 21% oxygen) will still get you 100% DO.
Dissolved oxygen % is based on equilibrium with the atmosphere, which is 21% oxygen. Under normal circumstances (in other words, excepting temporary special conditions like rapid temperature changes), unless pure oxygen is being injected into a tank, good aeration (through surface turbulence created by filters, airstone, etc.) will balance dissolved oxygen with atmospheric oxygen, what's called 100% dissolved oxygen. So with good aeration and water quality, short of testing with DO test equipment, you can assume you're at or near 100%. 100% is within the range the studies I've seen say is optimal for fish growth (typically 80-120%).
The aquaculture experiments test for higher than 100% DO, which is possible because photosynthesis or direct oxygen injection can add dissolved oxygen to make it higher than atmospheric oxygen. Meanwhile, in most of our tanks, "aeration" is still exchanging gases with the atmosphere-- trending down toward 100% if you have plants adding 'extra' oxygen. I don't know this, but it seems reasonable that a planted tank with light, little, or no water flow could exceed 100% DO (daytime). Otherwise, I expect most of our tanks that have good aeration are at or near 100%. In other words, going beyond good aeration to add extra' aeration (in effect, exchanging more air with the atmosphere, still at 21% oxygen) will still get you 100% DO.
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