OMG RUSHER!!!!!! AHHHH
First:
LFS is a business, they want money, what are the chances they actually care about the fish.... Ok they may look good in the tanks at the store, but those tanks are probably mature and none of those fish are probably going to be there long term. So what if you didnt see any dead fish, employees can take the dead fish out....
Second:
You, killed your fish, dont put the blame on your powerhead. They were weakened by the nitrite and/or ammonia and then they either died and got sucked in, or were really really weak and got sucked in. Either way i think you need to accept the fact that you killed them.
Third: Fish cycles work, heck ive heard of people peeing in there tanks to cycle it, as long as you add ammonia to the tank it can start to cycle. BUT, that doesnt mean its the right thing to do.
fourth: Let me ask you, what made you think you needed a cleanup crew in the first place? Diatoms? There normal, dont like them, scrape them off, dont put something in there to get rid of it, get rid of it yourself, small amounts of ammonia and nitrite wont hurt your hand at all, but it can kill a hermit or snail. Sometimes we shouldnt let nature do its work and we should butt in.
Lastly: you only hear what you want to hear, so chances are what i just said will go in one ear and come out the other since its not what you want to hear.
I dont see why we should pity him since he is 13, im 14, i dont want anyone to pity me if i did something wrong just because i was young, that gives me an excuse to not do whats right just because im young.