Let me just say this about HOB
vs sump. I have a single bak pak skimmer with a RIO 800 and producing good dark tea green colored skimmate. Now in theory this should NOT be able to keep up with a RIO 1700 pushing into a CPR SR4. However, I had to send the SR4 back due to a mfg problem with the bulkhead. Anyway, I placed the Bak Pak back into my tank (75G) after about 2.5 weeks. The hair algea was starting to take major root. 2 days after efficient skimming and its starting to disappear..from places it was before! So, either the SR4 sucks somehow, even though it was skimming its nurtz off or there is something to be seen yet as far as a skimmer in sump vs hob
. it seems to me that the smaller skimmer is kicking but and taking names because its in the main tank drawing water from the water column directly. This where as a skimmer in sump is taking water (at least in my case) from a 'skim box' attached to an overflow. I honestly think that the best place for a skimmer after this observation is *in* the tank. At least the pump that feeds it should be drawing water from the main tanks water column, not whatever happens to spill over. My observation.
Best of luck.