The acceptable GPH flow rate is any where between 4 to 10 times the volume of the tank. Don't forget to consider the head loss of your pump if water has to go up. But I don't believe that higher GPH means better filtering there's more to it than flow rate, but of course with the same sat up a tank with higher flow rate will filter better.muckieman;1243402; said:how did you figure out what isze pump was needed. and any updates.