Return pump speed math

[cnjcpb]

Here is the math:
400 GPH max pump
Speed 1 = 30%
Speed 20 (max) = 100%

If I’m running at speed 4 what % is that?

I am getting somewhere around 176 gph?

Also I have an AIO 26 gallon tank with an overflow and a small intake at the bottom of the tank about an inch above the sand. It’s 17” from the top of the tank. Will this create head pressure?

 

[OutColdCRNA]

My best guess 44% and 176 gph.