I would recommend at least an 18x18x18 exo terra for two arzureus. They are more terrestrial but enjoy climbing. The substrate would have to be at least 5-6 inches when properly layered. Water or not the tank just wont be able to house the darts properly. Sorry . I do know where your coming from as i have the exact same tank and was so excited to get to use it but i want my frogs to be happy so i will probably use it as a hospital tank or put fire bellies or something in mine.