I had a nice long answer all typed out for you but my computer froze so here it is condensed (I am trying to learn to be mor concise anyway).
If this is an emergency - your fish are hovering near the top of the water or gulping air from the top, turning over or swimming around really fast & crazily - do an immediate water change of 50% with dechlorinated water that is from the same source as your original water.
Then tommorow go get some anacharis or hornwort from the
LFS & check to make sure it doesn't have snails or snail eggs & throw it in there. Either will help absorb nitrogenous wastes like ammonia nitrites & nitrates (the 1st 2 will really stress your fish out as they are highly toxic). The plants will also add oxygen to the water.
The balls are bioballs which is your biological filter. My guess is that for some reason it has not finished cycling so you are getting a buildup of nitrites. Basically cycling is developing a colony of bacteria that make very toxic ammonia into nitrites & then relatively harmless nitrates. If you aren't sure what cycling is all about go to "search" at the top of this page & read up on it. It is critical to the health of your fish.
People will want to know
1) the numbers for your water chemistry. You can get them checked at the
LFS tommorow (most will do it for free). You need to know ammonia, nitrites, pH,
KH, &
GH & if possible nitrates & phosphates (if they say they are fine ask them what the levels are).
2) how fast your water is circulating through your filter in
GPH & what kind of a filter it is. (most likely the sponge is a mechanical filter to remove debris before the water goes to the more fine grain filters [cylinders]) Your manual will probably tell you exactly what everything does & how it should be set up.
3) if you have added anything new recently (water conditioner, fish, decorations, spilled something into the tank, etc.)
4) if you are doing regular water changes & how large they usually are in aproximate % of the total 24 gallons
5) what kind of fish you have & why you think they ar lacking air (what behaviors specifically)
6) what decorations & or live plants you have in the aquarium & what your substrate is (sand, gravel, etc.)
7) how much, how often, & what you feed your fish
I know it seems like a pain to describe all this but it will really help us figure out what the problem is.
Best of Luck.
HTH. & Welcome to Aquarium Advice
