Yeah...A 12X12X18 is only 11 gallons. That's going to be much too small for 4 frogs. You could get the next size up which is 18X18X24. That one is 33 gallons and would work for your frogs. I usually like at least 10 gallons per frog but is does get pricey on the larger tanks. You could consider turning a 40 gallon verticle, but there would be considerable modification for the door and ventilation. You could also check for larger tanks on craigs list. You'd be amazed at some of the deals that come up on there.