Sump Return Pump

[Jasmine]

How many litres per hour should I be looking at for a 680ish litre tank and a three foot sump?

[kiwiplymouth]

I would recommend at least 7-8 times the volume of the tank.

I have an 8000lph pump in my 1000L tank.

Be aware that the pumps capability will decrease as the height that it needs to pump the water increases.

[Jasmine]

Ah so I was right in looking at a 5000 litre/phour pump? The lady at the pet store seemed to think it was a bit overkill.

[Ira]

Ah so I was right in looking at a 5000 litre/phour pump? The lady at the pet store seemed to think it was a bit overkill.

Nope, not overkill it's about right. You'll lose 1000-2000lph because, unlike cannister filters, they are working against head pressure pumping back up to the tank. So you'll be probably at around 4000lph before you even take into account frictional losses, restriction from any spray bar, etc.

[suphew]

The quality of the pump also makes a huge difference to how well it will pump up hill. Once you have an idea of the pump you want check the box for an output curve or failing that check the net. Every resonable pump will have one. To save having to do all the height and fiction loss calculations I find working on the rough distance from the high water level in your sump to the high water level in your display, plus half again (for fiction losses in pipes) will give you a good enough number to work with, this usually equates to about 1.5-2 meters of head height.