If a fish is hovering near a water flow or near the surface, it may need more oxygen. If it grows listless, same thing.
Ich can cause this behavior, by affecting oxygen intake by the gills; but very, very often the tank is just oxygen-short.
Tangs and angels need more than most aquarium fish: they're like jet engines, consuming it like crazy. Those species will 'complain' first, or may mysteriously start to fail...another very good reason not to stock tangs in a small tank.
Over-warm water contains less oxygen. 80 is a good mean temperature to stay to.
Everybody knows that plants give off oxygen and absorb co2. But did you know that they do the reverse after the lights go out? At night they suck oxygen out of the water and give off co2. A really dense algae growth can do more than look bad: it can hurt your fish.
To increase oxygen, increase flow. Your tank may need a second pump. It does not need a lid anywhere in the system. Let it breathe. If you have jumpers, take measures like a high riser or eggcrate.
HTH.
Ich can cause this behavior, by affecting oxygen intake by the gills; but very, very often the tank is just oxygen-short.
Tangs and angels need more than most aquarium fish: they're like jet engines, consuming it like crazy. Those species will 'complain' first, or may mysteriously start to fail...another very good reason not to stock tangs in a small tank.
Over-warm water contains less oxygen. 80 is a good mean temperature to stay to.
Everybody knows that plants give off oxygen and absorb co2. But did you know that they do the reverse after the lights go out? At night they suck oxygen out of the water and give off co2. A really dense algae growth can do more than look bad: it can hurt your fish.
To increase oxygen, increase flow. Your tank may need a second pump. It does not need a lid anywhere in the system. Let it breathe. If you have jumpers, take measures like a high riser or eggcrate.
HTH.