I have a phosban reactor that ended up being used pretty much for carbon only but always had problems with the carbon getting packed at the top of the reactor and causing increasing backpressure on the inlet side. I read somewhere of a test of phosphate content of different brands of carbon and the seachem matrix carbon turned out to leach the lowest levels of phosphates so when at pet store today I bought some. The cool thing is since it is round pellets it does not end up getting packed at the top of my phosban reactor and water flow through the carbon is even and good so if anyone uses their phosban reactor for carbon and has problems with it getting packed at the top you might give the matrix stuff a try. Also I was able to increase the flow to around 200gph through the reactor since there is no phosban in it at the moment.