Pumps/power heads for marine/reef aquariums, how to work out the amount of water getting to your tank.

When using a power head return pump, for the flow back up to your aquarium from your sump/external filter, the way to test if your pump is suited is to firstly read the out put and height it is capable of before buying written on the pump or its container it came in.
Best to buy a more powerful one then your needs.
Most pumps have an adjustment on them to turn down out put if too great, if not, just reduce a section of the return pipe in diameter, that will lower the out put pressure to the tank.

Then to test its actual out put and height it is capable of pushing the water up to, get the hose you need for the return pump, put it on that pump and maybe an electrical tie to tie it it to that pumps exit to make sure it does not come off.
The pvc pipe should be over the length you need from sump to tank for testing.

Now get a bucket of saltwater and sit the pump in it, this may make a mess so do it over soil oo a sink or in a shower recess.
Keep the non-pump end of that hose at the height it needs to be as it returns to your tank and a one litre container in your hands.
Have a clock or timer near by to look at, something that shows seconds on it.

Hold end of hose over that one litre container,then turn on pump for 15 seconds, then turn off pump.
Now what is in that container, multiply it by 4, then by 60, you now know how that pump will work at what rate of litres per hour at your tanks height.