You can use both at the same time BUT, I think that should be for an experienced reefer(if you are, Im sorry). IMO, to use both correctly, you should be aware of how much Cal your tank comsumes and the consquences of a possible OD and how to "fix" it. If your not exp., I would do more research before diving into it. Luna _________ 9YR OLD 90G 30G w/d Mag18 150G skimmer 692w MH,yel&kole tang,foxface,midas&convict blenny,B&G chromies,Blk/yel fin chromie blackcap,nemo,neon goby,6line; Blastomussa Merleti,Acan ,BUBBLE,Torch,LTA, Goniopora(2), Acropora(2),Brain, Moon, assort zoas, yel& G star polyps, R&G open brain, P&B ricordia, montiporas, cup&candy corals, enias,B/G mush,flower ane(2), cherry red mussa, dusters,cleaning crew  |