I have seen videos for fish tanks that have crabs but they need air so the person makes a container that goes underneath the water that they fill with air somehow so that crab can survive I am just wondering how to get the air down and keep it in there without letting it just escape into the water
Your thinking of basically a bell diffuser on a co2 set up but filled with air instead of co2. You could keep it on the glass with suction cups and pump air into it with a simple air pump but the air will diffuse into the water so you would have to refill it often