I am running 2 socks, i have my 325 draining into 1 that I change when it is over flowing, generally once a week. I have another on the drain for my frag tank b4 it goes back into my sump, i change that one when i change the other. I currently have 0 nitrates and 0.02 po3.
Im not sure why people claim they cause nitrates to rise? I think if your over feeding that wasted food decaying in the sock will cause a rise in nitrates.
When i first got into this hobby i didnt run any socks or floss. I noticed, as mentioned above i had alot of floating stuff that made the tank look cloudy. I started to use the socks and i was changing them out every 2 days because they were overflowing. Now i am running approx 4500gph through 1-7" sock that i change once a week.