Well, i didn't wash the old gravel because i figured it would wash off the beneficial bacteria therefore rendering it useless, but i guess i was wrong. the smell did go away by the time i got home that night but i'll post in here again if it comes back. for future reference i feed them massivore, frozen carnivore food, and algae wafers for the pleco. and the only food the stays at the bottom is the few pellets i leave for my channel, but he finds them relatively quick so i just sit and watch and wait for him to find them (i leave them all in a corner).