Yea you are right, My very first tank I used a to fine sand on and had a bunch of loaches, who LOVED to stir up the sand and it got sucked up into the impellor and made a horrible griding noise. I returned the penguin and started using cannisters. On my latest tank, a budget minded one, I got another penguin filter because I do like them reguardless of the sand issue, and have had no problems with the powerhead, filter, and sand as long as the powerhead wasn't blowing directly into the sand. I just needed a little extra water flow to pick up the poo a Sorubim Lima can drop all over tank.