Depending on type of tank, it can range between 10x to 20x of flow per tank volume. So your lower and upper limits for this example will be:
10 X 55 = 550gph
20 X 55 = 1100gph
If your pump is actually pumping 75gph, or if it is rated at 75gph that would have an effect...because once you add your head height to it, that flow rate drops....let's just say for the time being it is 75gph. And which Nano did you get 285 or 425? Well we can do both.
75+285 = 360gph
75+425 = 500gph
Penguin power heads come in 2 varieties 145gph and 170gph
75+285+145 = 505gph
75+425+145 = 645gph
75+285+170 = 530gph
75+425+170 = 670gph
Well there ya have it. personally I would get another Koralia myself. Hopefully you got the 425. Couple that another 425 that would be a nice 850gph with the 75gph from the return getting you to 925gph, which would be a nice amount. Even with a couple 285s you'd be in the lower end of the middle ground...around 645gph...not bad, but the 925 is a little more appealing.
The other thing to keep in mind is the Koralia flow is alot different that flow from a PH. PH flow is very directional and aggressive compared to the Koralia flow which is wider and more gentle. Hope that helps!!
