Nerites are more algae eaters than detritus eaters, so I'm not so sure they'd be effective as a clean up crew. That said, if you want to try them, I stocked my 65 at a ratio of 1 for every 5 gallons. You could probably increase that to 1 for every 3 gallons. Take this as you will, but I think trumpet snails or ramshorn snails might be more in line with what you're looking for. Problem with those is possible population explosion. My $.02.