Problem Stabalizing Alk

So heres the story a few weeks ago my green birds nest colony tips started dieing so i started testing, my mag tested at 1250, ca 400, kh 5, and SG 1.023 so i started dosing using BRS 2 part solution. I dosed mag trying to get it around 1350, alk to 10, and ca to 420, but my mag never would go up and if it did it wouldnt stay there along with my alk but the ca would stay fine. I ended up buying another mag test for a friend and cross tested and this one said my tank was at 1600, i for got to mention that after my last mag dose my colar polyps started receeding, and my alk would go down up to 2 pts a day if i didnt keep dosing until it would drop to 5 or 6 again so as of now my tank it at ca 420 alk 8 mag 1500 and SG 1.023 I just dont understand why my alk is such a pain and why all my coral polyps are sucked in in my main tank when i try making the parameters good maybe too much fluctuation the past few weeks? Also I have a frag tank plumbed into the same system the only difference is it runs 4 T5's instead of MH. Any advice would be nice because im confused. Oh and the polyps come out after the lights go out at night still.

 

D J man

Im no expert on chemisty

but - Inwall75 once explained this subject in a way that was easy for me to understand

think of it as marbles of different colours
(red for MG, Blue for Alk and yellow for Calcium)

the bowl for the marbles is the specific gravity - the sum of all the ions held in solution

your SG at 1.023 - is struggling to maintain all the Ions you want to keep in solution
hence your Alk is possibly staying low, due to the levels of Calcium you have achieved

basically, as you add more yellow marbles, some of the blue marbles are being pushed out of the bowl

IMO
if you increase your SG to 1.025 and then retest (find out where that leaves you)
safest way to increase SG would be to make up a bacth of SW at 1.025 and use that to replace evaporated water until you get the tank up t01.025

you should find you have less issues maintaining the target parameters you have set
once you have reached an SG that allows you to maintain all the ions you want in the solution

Steve