everyday i wake up and check out the tank...about 3x a week for the past month i always notice that one of my stomatellas are on their back kinda curled up dead. Then i move them and they start trying to right side up themselves. is this normal for them to do this every couple of days? is someone picking on them [sixline maybe] and then when they fall they cannot right side. should i get rid of them before one of them dies and goes unnoticed and fouls the tank [solana 34gal]?