Ca Mg pKa all low, pH high(er)

brianw3185 · Jul 15, 2019

Hi, have a 36 BF, about 25 lb live rock, 2- powerhead undergravel, hob mechanical carbon filter, definitely not overstocked ( 1- green mandarin, 1-long nose hawkfish, 1- lubbocks fairy wrasse), tank parameters have been stable until now.
I was not testing for Mg and Ca til this week, so, in the past my pKa = 8, pH= 8.1 as of he water change two weeks ago, but now the pKa = 7, pH =8.3-8.4, Ca = 375 and Mg =1150. Also my R.I. went from 1.025 to 1.023.

Please help me, tell me what's going on, thank you all!

JustAnotherNanoTank · Jul 15, 2019

Well it sounds like your salinity is low too. Did you add a large amount of top off water recently?

brianw3185 · Jul 16, 2019

No, I add small amounts every couple of days, I have a glass top. I have had stable parameters for months, except as I said the Mg/Ca which I just started testing. I am going to retest everything, but I don't know what parameter(s) to adjust first, if at all. I am at a complete dead loss as to how this happened and what to do next, I just don't want to overreact and do something stupid. Thanks

JimWelsh · Jul 16, 2019

BeejReef · Jul 16, 2019

Nothing is crazily out of order.

Your alkalinity, calcium, and magnesium are all a little bit low. So is your salinity.

First, I would slowly adjust your salinity back to 1.025-6. This should have the effect of raising the other figures as well.
You can do this by performing water changes with slightly saltier water. Probably the most common way is to top of with saltwater, or top off 1/2 saltwater and 1/2 RODI water for a few days until your salinity is back to where you want it.

Once you've done that, you can re-test and adjust your calcium, alkalinity, and magnesium with water changes, dosing.... whatever method you're using.