mulron
Aquarium Advice Activist
Not sure if you figured out what size hole you need yet but I found this on another site. Might help ya. http://reefcentral.com/calc/drain.php
actually the cpr siphon's GPH values are maximum values, tehy can siphon any number of GPH less than the max.Yokhannan said:d9hp, CPR's smallest overflow does 300 GPH of flow-rate.... That means it would be turning over your tiny little 7 gallon tank 48.9 times an hour 8O Perhaps a DYI project would be better