A lot of people are using it in nano tanks if they dont run a skimmer, some even use it if they do (like me). It's another way of removing DOM (Disoloved Organic Matter).
I did a little test on my tank. I ran my tank for a month with my skimmer and with purigen and over 7 days got 3/4 of cup of gunk, I then ran my skimmer for a month without the purigen and had to empty my skimmer cup after 4 days, I then reverted back to the skimmer/purigen mix and it returned to skimming around 3/4 cupful of gunk over 7 days.
I'm intrigued. Will go down to my LFS today and will give it a try. I am planning to rip out all of my bioballs, wool etc and will just run my canister with some purigen and bit of live rock.
Most people really only have on average 15-20x turnover. It is very hard (near impossible) to get the turnover required to mimic a real reef without blowing sand all over your tank. Plus most people try to limit the amount of powerheads in the tank for asthetic reasons and usually find out about closed loop systems after they have already setup the tank and can't drill them for closed loop.
For your tank, I would suggest something like 2 Koralia3 powerheads. If you have a lot of $ then tunze powerheads are the top of the line IMO but beyond my budget.
Personally, in my sump, I use both Purigen and Chemi-pure along with a phosphate reactor with rowas media.
My LFS has just changed managers and new prices are ridiculous. Supplements that used to cost $19 now $42. So will search online for better prices. Anyone know of good aussie sites?