Dosing Alk, how do you do it? - Coral issues

[CanuckReefer]

So I'm pretty depressed about my tank lately. I've lost most of my corals, never had many to begin with... I have spent lots of money on corals only to have them die usually a month later.

-So it's a 90G with 2- 120watt led lights, skimmer works good, I have carbon and GFO in the sump, water change every 4 weeks, Ph7.9, Ca400, Mg1350,Phos0.08, Alk is all over the place.
I check everything weekly and I manually dose baking soda to maintain alk. I am adding usually 2 tblsp a week just to maintain alk at around 7-8. I think the fluctuations are what my problem is.

I have tons of coralline, I have zoas growing like crazy, GSP, Kenya tree, Xenia but that's pretty much it. I can't keep,birdsnest, torches, Duncan's, or any hard coral. The bases always start to deteriorate over time and the coral inside usually dies.

I have removed all fish for QT and am going fishless for 8 weeks to rid itch. In this time I want to get my minerals sorted out.

What is the easiest way to constantly dose alk so I can keep it constant. And should I be using baking soda to maintain alk?

Also I use rodi water and my tank is a little over a yr old.


Any help is appreciated, thanks!