a 2nd pump to recirculate rez is absolutely imperative when using organic hydro nutes...not so much when using something clean like 3-part.

good idea to start thread, but, I agree with Z about the heat issue. I have a helpful hint on the subject. I have found that the heat from a submersible pump isn't as damaging in a bigger deeper reservoir, requiring a higher volume of solution. also. I use 110gph pumps, and they don't generate as much heat as bigger...say 256 or 500+.

one last note. You can also balance the heat issue by have a 15 minute off time each hour. I didn't see a loss of growth when I did this, but my rez cooled down to tolerable levels, due to pump cooling down each hour.

hope this helps...It's late. peace