Does Carbonate Hardness Affect Ca and Mg Levels

[Greg Vontz]

Due to the use of an carbonate hardness supplement, my dKH levels have risen to 12.8; I have since stopped using the additive and am targeting a dKH in the range of 9 -10. I have been testing my water using Salifert test kits. My questions goes to the possible suppression of Ca and Mg levels as measured by Salifert test kits when the dKH is so high. I am struggling to keep my Ca above 400 and my Mg above 1200 ppm. Both Ca and Mg levels seem to be slightly depressed in my tank, despite using a calcium reactor that is well tuned and adding a quality Mg supplement. My reef tank is just getting established at 5 months of age and is lightly stocked so it seems unlikely that the tanks inhabitants are causing the depeltion. Can anyone shed any light on the possible affects of high carbonate hardness on analytical results for other cations?

 

[Billybeau1]

[welcome]

Give these a read and come back with more questions if you need.

The relationship between calcium, alkalinity, magnesium and pH
http://reefkeeping.com/issues/2006-06/rhf/index.php

and

When do Calcium and Alkalinity not balance
http://reefkeeping.com/issues/2004-12/rhf/index.htm

There are also a few more great articles on the subject in the Reef Chemistry articles tread at the top of the page.

Good luck

 

[Greg Vontz]

Thanks so much

 

[Billybeau1]

:thumbsup:

 

[marsh]

In general, Mg because of its' much higher concentration, will dominant a tanks chemistry in regards to Mg, Ca, and Inorganic Carbon (H2CO3, HCO3-, CO3--). At 7-11 dKH or 125-200 ppm calcium carbonate equivalents is far out dominated by Mg 1200 ppm for ionic pairing.

It takes a bunch of Mg to increase a tank's Mg levels. You may also want to make sure sg is in the 1.025-1.026 range.

 

[marsh]

In general, Mg because of its' much higher concentration, will dominant a tanks chemistry in regards to Mg, Ca, and Inorganic Carbon (H2CO3, HCO3-, CO3--). At 7-11 dKH or 125-200 ppm calcium carbonate equivalents is far out dominated by Mg 1200 ppm for ionic pairing.

It takes a bunch of Mg to increase a tank's Mg levels. You may also want to make sure sg is in the 1.025-1.026 range.

 

[Boomer]

Running high dKH can lower the Ca++ and Mg++ by abitoic precipitation but you are not all that high. The bigger question is what are you adding as sups', not all sup's are the same, as some can cause issues more than others.

My questions goes to the possible suppression of Ca and Mg levels as measured by Salifert test kits when the dKH is so high.

Meaning you think the kit is not measuring the Ca++ and Mg++ levels correctly due to high dKH. No, this should not be an issue at all.

Usually such problems as you have are from an ionic imbalance which can only be corrected by a couple of large water changes. These are usually created when one keeps trying different sup's which are chemically different, in a hopeful cause this sup will fix things. Bad Idea

I am struggling to keep my Ca above 400 and my Mg above 1200 ppm.


But what do you mean by that ? What are your daily needs i.e., how much do you drop in Ca++ and Mg++ /day ? Also what is your pH and salinity.

 

[Greg Vontz]

Boomer:

pH is 8.3 during the day and it drops a little at night. SG is 1.025. From the responses I have read it seems like my high alkalinity levels are supressing the ppm concentration I am trying to hit on my calcium levels. It was also helpful to get the perspective that you have to add a lot of Mg to raise the concentation. I tried to get by with an inexpensive salt mix that was deficient in Mg and I am now learning how much Mg I have to put back into a 175 gal tank.

I am going to do a large water change with quality salt and see if that doesn't lower my alkalinity and improve my Mg levels. Once the alkalinity levels are in the range of 9 - 10 I would expect I can readily get my Ca levels to 425 ppm. Hopefully the Mg levels will then be higher and thereafter requre only minimal replacement due to consumption.

Thanks for the input.

 

[Boomer]

Ok Greg

However, you high Alk should not really have that much to do with it but it *may. Usually WC fix things

 

[Henry Bowman]

Greg,

You posted that you are / were using a Calcium reactor AND adding a Carbonate Hardness suplement..... This is why your dKH readings are high. The Ca Reactor adds to the alk / hardness of the tank also. You noted that you stopped adding the supplement (Good Idea) and doing a water change (also a good idea).

I dont think that 12.8 is THAT high. Definitely not dangerous.

Without adding the supplement it should drop in a few days on its own unless your reactor is set to produce more than tank demand. (I dont think this is the case since your dKH reading is not higher than you indicated.) What is more dangerous to SPS corals is drastic or quick change in dKH.

 

[Boomer]

Just to add some more. Before you even think of running or turning on a Ca++ reactor, Ca++, Mg++ , pH and Alk should be in line so you can see what the Ca++ reactor is giving you and THEN Sup as needed for pH, Alk, Mg++ and Ca++.