Series of pumps

I have a 180 GPH submerged pump in a resivoir and a 370 GPH inline pump. Becuase of the extra waterblocks and radiators I just put in, I need that stronger pump. I was thinking of running that 180 GPH pump directly to the 370 GPH pump because the 180 is in my only resivoir.
Can I run them like this or is the differences in power too much?
Will I have to buy a resivoir without a pump for it to work?

I tried my setup and there was nothing irregular.
Could it be harming either of my pumps?
Should I take one out of the loop?
I'm going to try and run them speeratly and see what temps I get.

Try listing the head pressure instead of the GPH. A pump might do 370GPH at 0' head, but at let's say 3' head, it might only do like 50GPH.