its a 20 gal tank (24x12x ?) with a emperor 400 and no skimmer, i have a little seaclone (venturi driven) for it but it appears that the goose neck intake tube that came with it (i bought it used) is home made and doesnt fit correctly. I'll add a powerhead with a venturi to add some oxygen to see if that is the problem. They are in what is going to be my QT once my main tank is ready for fish. The clowns and cherub angel seem to be doing just fine, are inverts more sensitive to low O2 levels? Thanks!