So gravity drains from overflows, to socks. From socks to bio tower. Then out to Ultima and back then blasted back to tank?
Yes you have it correct.
Questions.......
Does the water drain just from the surface of the tank or does it pick up from the lower level too?
Water drains from surface of tank, The returns angle down to floor which pushes water from bottom up and out the overflows.
Why 3 pumps? Are they all constantly used for returning water or is one or more just used for backflushing the Ultima?
Two 10000 GPH pumps return into tank, one goes thru UV and into left corner return and other goes thru ULTIMA and into the right corner return. The third pump is 8000 GPH amd is only for the skimmer system it returns into the sump. Bio-tower and chiller have has seperate 4000 GPH pumps both return into sump as well.
What micron are the socks going to be?
Since tank is salt water they will be 200 micron.
Is there a rule of thumb for how many socks per set GPH? How did you come up with the number of socks being used?
It all depends on mircon size, These socks can do about 100 GPM each. I always try double the GPH thru returns to make sure the socks can handle flow.
Sorry for all the questions Mike but I find the filtration part of this hobby to almost be more interesting then the actaul livestock. To me the system can be just as impressive as what it supports.