Your title begs a question, yet your post did not expand.
I looked for a tank thread. Is this sump for your 120G display that is 3 years set up?
Consider removing filter floss and allow cascading water to fall over a wet/submerged section of rubble. Degassing of water is very important in moving oxygen, nitrogen and carbon dioxide fron a gas to saturated in water. In the open area of sump, get some real live rock to inoculate cryptic sponges in a dark sump.
Also, by removing the filter floss, detritus will begin to settle in open area of your sump. This is energy rich carbon that fuels the microbial loop. Consider what PaulB says about MULM.
I think one of the most important, and least understood or mentioned things in a reef tank is "mulm". That stuff that grows in the dark portions of a tank if it is set up long enough. "Mulm" is a combination of algae, sponges, bacteria, pods, worms, detritus, poop and any thing else that can be p...
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