ok so heres the thing, if youre going to doubleup on media, the carbon will be exhausted long before the GFO. so you cant mix them together without either leaving the carbon too long, making it ineffective, or removing the GFO too soon, which is a waste and expensive. i would suggest running the carbon in a mesh bag so its easy to remove and replace after a shorter time period (ie. a week or two, or up to a month if that is your preference) and the GFO can stay in the reactor for 2-3 months.
when i ran my 90 gallon tank, i used a cup of carbon and a third of a 150g container of phosban. I dont use rowaphos because it strips the water too quickly and i lost a bunch of sps as a result. I now use GFO from bulk reef supply because its a better deal. most GFO comes with instructions on how much to use and i wouldn't run more than the recommended amount.
if you can try to have the reactor intake towards the end of the sump where the tank water enters and the reactor output near the sump return, that makes the most sense to me.
also be sure to run flow through the reactor slow enough so that the GFO does not move. you dont want it tumbling an creating a fine powder to disseminate throughout your tank as it breaks down. use the small valve that came with the reactor fir this on the reactor outflow line.
i think that covers it!
