cleaned out my canister filter this weekend and put in the first tray a blue pad followed by 3 white pads ,2nd try active carbon ,3rd tray bioballs and on top of the 3rd tray a white pad with a bag of seachem purigen 100ml. and my water is crystal clear now .
Purigen works, that's for sure, i am using it too. Is your tank fish only or a reef? If reef i would get rid of bioballs, they are nitrate factory, for fish only doesn't really matter.
I have used it in sump...works. No negative impact to skimmer that I could perceive.
Only thing I'm a bit suspect of now is using more than directed. I had appox 4 times the directed amount in my sump (more is better right LOL) and after about 4 months my N03 was imperceptible but P04 plentiful....meaning imbalanced. I had to take it out to get N03 back
It's supposed to absorb some Nitrates. If you use too much, it could cause cyano to start. You need good balance of nitrates and phosphates. The Bacterias that process phosphates use some nitrates in order to process phosphates.
I when I started I bought a FOWLR thinking 'no need to cycle the tank!', but I inherited a sand bed full of...uh, you know. And quickly I found I had N03 north of 100ppm and it was a lot of work to bring it down (3mo of weekly 50% water changes barely put a dent in it because the sand bed had reserves!).
Once I got it to 'normal' I did not recognize that my 'denitrate' approach was excessive...and I ended up with an imbalance and eventually cyano