Overflow and Return pump

Ok so I am new to all this and don't fully understand flow rates yet and this may sound dumb but I don't want to be wrong and throw money away but if a overflow is rated at lets say 300gph should the return pump be rated the same or higher ? and I am also bidding on a skimmer on ebay and the seller said it has a pump for it that is rated at 1200gph does the pump for the skimmer have anything to do with the rate of the return or overflow ? I don't want to keep bidding and have something to powerful for my 75g tank.

 

the overflow flow rate should be higher than your return's flow rate, or else your tank would overflow. the water should be drained out faster than it is returned.

not sure about measuring overflow flow rates, but i make sure that my pvc's & tubings for the overflow is bigger than for the return. i.e. now i have 2 x 1" in my overflow and only a single 1" pipe on my return.

my other tank has a single 1" for the overflow and a 1/2" for the return.

and no, the pump for the skimmer isn't connected to your tank's flow rate. it only describes how fast it pumps water to the skimmer itself.

hope that helps!

 

When buying a return pump you need to consider the head loss due to the vertical lift and the fittings and tubing or pipe. Most pumps are rated at 0 feet of head for their maximum GPH and will have a pump curve or head loss chart which shows what it will pump at say 5 feet of head which is a pretty common number taking into account the losses from both the lift and the line loss.

The overflow box should always be larger than the return pump minus head loss. The skimmer is strictly recirculation inside the skimmer or feed rate and has nothing to do with circulation in the display tank which is achieved with the sump return, powerheads and possibly a closed loop.