Raising Mg also Raises Calcium?

[CarolinaReefs]

My Mg was 1240 last weekend. Calcium was at 411. I added BRS Mag/Chloride - Mag/Sulfate Mix to raise Mg this week (160ml over 4 days). I tested all of my params today and Mg is up to 1300 and Ca is at 510. I have not dosed any additional Ca to the system. I do run a Doser that doses Ca 40ml per day but that wasn't enough to maintain Ca at 440 as my Ca had been slipping down.

Will the increase in Mg "free up" Ca that is in the system and cause Ca to rise like this? or is this not possible?

Mg Tested with Red Sea Pro kit.
Ca tested with Hannah Colorimeter.

 

[Randy Holmes-Farley Verified Community Expert]

How much calcium solution dosed in that time, and how much alkalinity?

Testing error is the most likely explanation.

 

[CarolinaReefs]

My Alk stays consistent @ 9 dKh I dose 8ml per Day Soda Ash Mix.

So over the last seven days I have dosed :
160ml Mg Solution
56ml Alk Solution
280ml Ca Solution

dKh Constant @ 9
Ca 411 to 510
Mg 1240 to 1300

 

[rockskimmerflow]

I'd bet it's the 280ml Calcium/56ml alkalinity solution ratio that's the culprit. The added mag possibly stopped precipitation of all that excess calcium addition. Assuming a balanced 2 part mix is being added I can't fathom a disparity in dose volumes like 280/56 being feasible. Calcium would probably shoot up even faster if not for precipitation effects.

 

[CarolinaReefs]

I modified my dosing pump this morning and cut the Ca dose in half. I'll re-check next weekend and see how it looks.

 

[Randy Holmes-Farley Verified Community Expert]

What size tank is this?

Then we can calculate what calcium rise you'd expect from that amount of calcium solution, minus the amount that went into calcium carbonate (which we get from the alkalinity additions).

 

[CarolinaReefs]

It is a 75 Gal with 30 Gal sump. I estimate total volume @ 85-95 Gallons

 

[Randy Holmes-Farley Verified Community Expert]

So assuming you made the solutions per my directions (BRS directions), then in the past 7 days you added only 30 ppm of calcium. Any rise that is greatly larger than this is likely testing error. The magnesium addition itself didn't cause any unusual impact that would cause calcium to rise more than this (assuming it wasn't a calcium additive by mistake )

 

[CarolinaReefs]

Thanks for the input Guys. I'm going to retest Ca, Mg, Alk tomorrow afternoon.

 

[Randy Holmes-Farley Verified Community Expert]

OK sounds good.

Happy Reefing.