I have had a 55 gal. aquarium for years. I wish I didn't let it go the last time I moved. But if you are keeping tropical fish the rule of thumb is about 3/4"s of fish per gallon. So a 55 gallon aquarium could keep, in residence, for looking at about 70" of fish. I had two filters, an under gravel and one on the back side. I only had to clean it every 6 months.

Minnows are very hardy and will do fine but you'll have to keep an eye on them insuring they don't get too stressed. If you fish regularly you will thin their numbers with every fishing trip. I've kept tuffies for over a month with no heater and feeding them Tetra-min fish food and dipping a half gal. of water out and putting back the same amount after aging it so the fluoride evaporates.

Grace/Peace, tuffynshiner