One of my bettas i guess has decided that just the tank isnt big enought for him. (its a 3 gallon tank) He likes to swim down the air tube and get under the gravel in the undergravel filter i have tried blocking the opening of the tube with wire but he just found a way in and couldnt get out. since his fins arent getting hurt i just took the wire off and let him play in the air bubbles
. after I took the wire off he swims in and out freely. he could be stuck in the undergravel filter if you have an airtube bigenough for him to swim down to the bottom?