Is it sufficient to only agitate the surface but not aerate the water?
I have a question concerning the filter in the aquarium, which is: Closing the hood pushes the filter downwards, so no air bubbles form any more, but the water surface only hss ripples. Now I would like to know if that is alright.
yes, this is completely alright.
Somebody said this was impossible: The fish would not get any air without bubbles being formed.
This is not correct, since the main amount of oxygen is taken up through the surface and not through aeration (only indirectly, as this of course also somewhat increases the surface). In other words: If the fish gasp for air at the surface without aeration, something is wrong in the aquarium (e.g. too many fish, too strong CO2 fertilization, cover panes that fit too tightly, excess water pollution, too high temperature, etc.), and in such cases it is of course advisable to remove the causes instead of only reducing the symptoms by aeration.
There are of course situations when aeration makes sense (e.g. during a disease treatment or in case of high temperatures during summer), but they are exceptions to the rule.
Dr. Bodo Schnell