How easy will it be to clean the pre-filter material?
Not cleaning it regularly (every couple of weeks) could result in a build-up of nitrates in the system over time... and if it's a PITA you won't do it as-requently-as-you-should.
Perhaps plumbing the two pre-filters in parallel so that you can take one offline and clean it without stopping the whole system?
Matt
There will be ball valves, and drains built into the system.
turn ball valve
open drain
take lid off
replace filter pad
put lid on
close drain
turn ball valve.
Should take about 5mins for both.
The filter socks will be catching most of the waste, these are just for polishing and pre-filtering of the bio-UV-chiller loop to make sure no trash ever gets in it.