Phosphate remover in cannister filter?

I have a canister that I run only carbon in,

no matter what I do with this tank I cannot get the phospate to 0.

Have checked RODI changed filters, have a very strong skimmer, have done major water changes. The tank is heavily stocked on corals, and I have come to the point that something mechanical needs to be done.

What kind of phos remover can go in the canister, and do I need a bag like the carbon

 

You definitely will need a bag. It will need to be fine mesh. Any brand of GFO will do. Do not stuff the bag full GFO needs to tumble to be effective and to keep it from clumping.

 

What kind of canister filter are you using? Also I would definitely look for the source of the po4.

 

I would really suggest running bio pellets. Do a search for a thread called carbon I believe and you find all the info you need.
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GFO media needs a fairly low flow rate or it grinds itself to dust. It also only requires about a tablespoon of media per 10 gallons of system water so a canister may be too big and have too much velocity or flow through it.

If you do choose to use a canister, stick the well rinsed media in a fine mesh bag then place it between two filter sponges so it does not tumble around and grind up. In a reactor you keep the flow to a minimum so the surface of the media just boils or moves slightly but not so much that it really tumbles.

 

I assume you are running your system without a sump. If you do though, you could just place the media bag with GFO right in to the sump, where it won't get ground up, as mentioned above. Or you could run bio-pellets in the canister loose and then use a thin filter pad from them getting out. Put it about 4 inches from the bottom with about 2 inches of pellets. then you could put your carbon in a bag above the pad.