Return Pump Help

[Liquitech]

Hi there I'm looking to find out the proper size for a return pump that will be providing flow to the following:

150 Gallon tank and dump.
1/4 HP Chiller that needs 600 GPH
2 - Vertex 1.5 Reactors (Carbon, Biopellets)

This pump needs to be also needs to be submersible.

Thanks in advance!

The return pump is located where the 1" goes down on the back right corner of the photo. There will probably be two 45 degree fittings being glued in before that 1" tee. Hope this photo helps!