Yeah it's sort of kind of a Spare but when I ordered my system my DI
canister came in chipped so I emailed the Seller and he said I will just send you out a New one... There was no questions asked. But when I started use the damaged canister it was still in good shape to use so I never changed it out. So now I have this brand new RO
canister that's just sitting around as a Spare but I know i can put it to use since they sent me a New Canister. That's all I am asking just to see if I can added another Filter to my existing RO
unit. ccCapt recommended use it as a GFO
but I could even use it as a Hang-ON back on my Aquarium and I don't have a Sump System. So i was just thinking to use this extra canister and build it to a 6 stage and be done with it...