I agree completely with garfy. However, I have seem plenty of folks who swear by overstocking. The downside to overstocking (besides the squabbling) is this: No matter how much filtration you add the end product of biological filtration is Nitrates, and filters to not effectively filter Nitrates. The only effective way to keep Nitrates in check is be doing partial water changes. So if you should choose to overstock, be prepared to do partial water changes frequently; perhaps multiple times weekly.