Hey look that my post.
I stand by what I said. And others have explained it too, its the problem with mechanical filters, same with socks. Check out the BrS TV video on socks and you'll see why they say mechanical filters need to be cleaned out every 3 days to really have an impact on nitrate management.
There are other reasons nitrates are high - the source can be many places - anywhere waste collect is a nutrient battery that'll release nutrient back into the system even if you don't feed. Could be your sand, your rock, your dirty sump, ur dirty overflow.
Cannisters are harder to clean and maintain with that optimal frequency than socks.
Mechanical filters doesn't reduce no3, it just collects dissolved food particles in 1 spot. IMO that in itself nit always good either bc leaving it floating in your water column means that your filter eaters and corals has more chance to capture and eat them. This will also increase your biodiversity and microfauna that leads to a more stable tank.
For this reason I don't even use socks.
All that extra food flowing in the water has resulted in a very biomass in my tank. I feed heavy daily, dose amino daily, feed reef roids every other night, and my no3 is barely over 2ppm and po4 at 0.02ppm. Tank is very mature now at 4 years.
Its all about "high through put" and knowing how nutrients travel thru your system.
No cannister, no sock, skimmer is used mainly for air exchange for the co2 scrubber (i just let the waste flow back into the sump bc that's still nutrient that feeds my fuge, filterfeeders and corals.
If you want to reduce no3. Go with algaes, they are one of the real no3 eaters.