 Re: Water Pump question
Depends on what you want it for, and what other equipment you have.
If it is the only pump, and you have lots of fish, and this is the filter, then a HOB filter is best figured at about 10 times the volume of the tank in gallons per hour, so a 10 gallon tank, filtered with a cartridge style HOB would require 100 gph. A 30 gallon needs 300 gph.
Similar set up, but canister filter might get by with 5x the tank volume.
Fewer fish? Less gph.
More decorations, plants and other obstructions to water flow, perhaps more gph, or use a couple of powerheads with very careful placement to avoid stagnant areas.
Hillstream tank, for example for certain Loaches start with 20x the tank volume, and all lined up to create the effect of a rushing mountain stream.
If you are using this as a pump to lift prepared water out of a bucket and into the tank after a water change then try at least 100 gph, the bucket on the floor and the tank at waist height will slow the water down so it does not rush into the tank and disturb the substrate or slosh the fish around. | 
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