Nano Tank Reboot! Help me with plumbing.

[ArialReef]

Hey all, it's been a while.

So, I have this 8 gallon tank that I neglected for a year because of a tank crash.

Today I decided that I'm going to reboot it! It's been a while so my reefing knowledge might be a little rusty.

Okay, so the display tank is an 8 gallon tank. I'm planning to add a 5 gallon sump. Currently, I have a 1200lph (sorry americans!) durso overflow and a 1600lph ac return pump. The pipe from the overflow goes straight down to the sump. The return line goes up around 4ft and has a total pipe length of 5ft and has 5 90° fittings. The problem is, with my current return pump, the water level in the sump gets way too low and the pump starts sucking air after a while. I'm not good with calculating head pressure and plumbing so any help would be appreciated!

Thanks!

 

[mcshams]

Do you have any valves on drain or return line? Oh, and while I'm American, I'm a scientist by trade, so the metric system is fine by me!

 

[ArialReef]

Do you have any valves on drain or return line? Oh, and while I'm American, I'm a scientist by trade, so the metric system is fine by me!

No valves or drain. It goes straight to the DT. It's kinda hard to find a valve as the pipe is a non-standard diameter (you know those cheap powerheads? I use a pipe that fits on the output opening)