For the first 2 weeks it is advisable to run it 18V, this gives parts a chance to wear in with less noise, they are considerably more noisy for the first 2 weeks. Also, be sure you put the rubber bumpons on the magnets, having the hard magnet surface in direct contact with the glass transmits much more noise.
The flow if you just submerge the wavebox and disconnect the controller at 24V would be 1450gph, since you are pulsing it very rapidly to produce a wave it never reaches this full potential but the gph of the wave will generally be much higher though this requires a fair amount of math to calculate. You first have to figure out the waves volume by taking the tanks length and width and multiplying it by the waves height in inches divided by 2. You then divide that by 231 and you get the volume of the wave in gallons. You then have to multiply that by the number of wave cycles in a minute and then by 60 to get the gallons per hour.