probably copepods, copepods make excellent food for picky eaters like seahorses. Mandarin gobies love them and they are essential to a reef tank adding biodiversity.
Opinions are like a lot of other things, so here is mine. The HOT is a nitrate generator like most canisters that are not properly maintained, although i do use one with the pleated filter and DE powder to polish water.
Ive used the Aqua-Clear filters for lots of applications for many years...
I have a breeder friend Liz, who has a fantastic setup for just water changes, storage barrels, all plumbed up to just open valves and get freshwater daily.
There is no way i would break that up. Buy cheap dry rock for your base, add some nice coraline coated pieces for seed and have an awesome display. Ive never seen nicer rock.