I actually talked to Russ today from Buckeye and I may very well end up with one and maybe two of the housings that will simply sit EMPTY. I overdid things just a tad. I figured I'd add another carbon filter but Russ told me there is no point. The carbon block I'm using is a high end block as it is. If I add more carbon it will not make the carbon last longer so I would end up simply changing an extra carbon filter every 6 months. Basically - throwing my money away. I also need to check with the water company and see if our city water even has chlorimines in it. If it doesn't, then I am simply wasting my time running Catalytic carbon as well. Now - IF I can find out from the city that they add phosphates or something like that then I could use a housing for a special filter to treat something like that and it would benefit the system.
BTW: Almost done with it. Only one more line to run. I have to get a drain line run the ceiling.

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150 gal Custom. Born 5/7/07. 50gal, 29gal, 20gal Sumps. 30gal Frag Tank. ETSS 800 Skimmer, Deltec APF600 Skimmer. PFO Solaris Lighting on Display and Frag Tank
My Tank Thread