Low ALK High Mg!!

[Afenstem26]

Hoping some of you on here can help me. I've been doing saltwater for about 8 years and hot out for about a year and now I have a 75g mixed reef with 20g sump. I have a BRS gfo reactor hooked up, only been on for about 2 weeks. Since I hooked it up my alk has been dropping.
My parameters are as follows:
SG-1.025
PHOS-.04
Mg-1600!?
Alk- 6.8
Calc-450
Nitrates-0
Temp-78-80
I do a weekly 10g water change with the ESV B-ionic salt mix.

I don't understand why my alk has been dropping all of the sudden. And also my mg is way higher than I like it. Any help would be appreciated.

Thanks.

 

[Afenstem26]

Anyone?

 

[kaskiles]

Try on chemistry forum.
I believe gfo might absorb a little alk...

 

[Afenstem26]

Thanks for the response. I will check there

 

[Reefin' Dude]

how old is your substrate? the older the substrate the more phosphates, the more bacteria, the more elemental carbon it needs to feed on the phosphates, the more carbonate it uses.

GFO is only removing the phosphates that get to the GFO. they have to come from somewhere, the bacteria in the substrate.

G~