When to replace gfo

[Scotty Fraiser]

How often do you replace Gfo in a reactor in a reef tank. If the answer is when phosphates rise approximately how long does that take? 110 gall reef with 35 gall sump. I am running 3 cups of Gfo in reactor and a little carbon.

[Marco V]

I have a 60g display and 30g sump and use 2 to 3 cup in my BRS reactor and swap that out every 2 -3 weeks. I'm probably wrong do so but haven't had any ill effects . I have my tank up a little over a year now but the reactor just the last six months .