[Unit134679]

I'm starting to notice that my fish stay at the top of the tank at the very surface. They seem inactive and don't seem hungry and would much rather "breath at the surface." I checked the chemicals and all seems ok. Not too sure what is happening since this is a first.

 

[Toby_H]

If they are mouthing the surface this is usually a sign of not enough oxygen...

The warmer the water is the less it will want to retain oxygen... often when a heater gets stuck "on" we notice the fish mouthing the surface (lack of oxygen) before we notice the warmer water...

The best way (I know of) to keep the water properly oxygenated is by creating surface agitation. This can be done with filter returns or by adding an airstone (the stone doesn't actually put the oxygen in the water, the bubbles create the surface agitation which allows a gas exchange).

 

[Number6]

the stone doesn't actually put the oxygen in the water, the bubbles create the surface agitation which allows a gas exchange.

We really should say that the bubbles do not put enough oxygen into the water... some O2 is added.

 

[PsYcHoTiC_MaDmAn]

another thing that an air stone does it it creates some water movement through the water column (especially if the airstone is right at the bottom)

so it adds extra oxygen via the surface agitation. however it also draws water up from the lower parts and oxygenates that.

though a small filter is more effective (IMO anyway) due to the higher turnovers, HOB can do it, (though I found the flow ends up pretty smooth and didnt create a lot of surface movement) but I prefer to use internals or spray-bars on externals. as the higher turnover + intake at the bottom of the tank leads to much more water movement.