If you're looking into opening a pet store, you would need much, much more than just 3 tanks totaling 85 gallons. There's a link here and on MFK with numerous tanks- a guy just closed his pet store and is liquidating his stock of equipment. As a side note, you cannot scrimp on cash if you actually intend on opening a pet store- you will need to shell out cash for decent stock, or shell out for breeding stock if you planned on raising your own fish to sell.