Dosing ? and help

[donkey77]

Ok i got a 90 reef with a 33g sump, iam using instant ocean reef salt, reg water changes, i grow some cheato in the sump also, i have a mixed tank of mostly LPS, lots of zoa's, lots of corals, I check my tanks parm and its using some of the elements, cal,alk, mag. I want to start using my 3 channel dosing unit, i got red sea abc reef foundation, Iam having a hard time judging how much my tank is using so iam going to start off with 20ml a day dose 8 times a day 7 days a week with a 10 min delay, what should i dose first
My coraline algae is not really growing great. what should i start off my mag at
I know its hit or miss with dosers, i don't want to over dose my tank so i will start off low and work my way up
any help
thanks