I'll add to the silica sand is harmless brigade here. I use play sand - the exact pre-washed kind you get from home depot. I've also used argonite sand in the past, and it was more abrassive by far than the silica play sand which is very rounded because your young child is expected to grind their bodily parts into it when playing.
Silica sand won't hurt your bottom feeders, will be silty at first and could clog up your filter at first (so what - wash everyting, take the impeller out and wash off the magnetic part of it and it's fine). Personally, I break down the filter and clean the impeller and all every few months (while keeping the filter media wet to keep all those nice biological friends alive), and the impeller is just as good as new despite the sand. I do keep the intake about 3 inches or so above the sand since my altispinosas sand sift a bit, and I'd use a prefilter if I had messier digging cichlids just so they wouldn't spit sand into the intake for fun which could cause your filter to clog up (I'd be less worried about the impeller breaking down and more worried about the sand clogging the area magnetic area which could cause your motor to overheat - and a convict or texas cichlid could easily spit argonite sand into the intake, too).
Eric