as long as your smart, you'll be fine with more than 'recommended' fish, i have 5 for now, but will get 6 with the addition of a mature perc in a few months. I have two filters and no skimmer. and i do monthly water changes, 3 of the fish have been in there for 10 -11 months. Mine dont produce much bioload though, keep that in mind when picking fish. and a lawnmower will need alot of rockwork with algae in a 30, i was gonna get one, but they produce ALOT of waste (raises bioload). firefish, shrimpgobies.... those produce very VERY little waste and barely contribute to bioload.