Ca low but Mg high. Ok to dose just Ca?

[NanoRox]

The chemistry of reef aquaria is not my strong suit so not sure how to interpret these results.  My corals look great and have been growing wonderfully.  Parameters have been stable but I have seen the Ca slowly decrease while Mg seems to stay at the high end.  My parameters today are as follows:

 

ph 8.0

salinity 1.026

alk 8.8

ca 375

Mg 1370

 

the Ca is too low but my mg is high.  I thought the two would decrease together.  

 

I am using a kalk additive to my ato that has added Ca and mg (Brightwell kalk +) so I was hopeful the two would remain in balance.  That does not appear to be the case.  

 

Suggestions?  Ok to just add a ca supplement? I think I will just slowly add ca (Red Sea part A) to get it up where I am happy.  Or should I switch to two part entirely since my corals appear to have switched into high gear?  Thanks for the input! 

[Clown79]

Mag is just fine. It's not high. I've had mine at 1500. 

Mag being low is an issue.

 

Ca is a tad low. Should be 380-450

 

Alk is fine.

 

I

Using 2 part dosers is far easier as you dose according to alk consumption and equal part of ca.

 

This keeps them balanced because as alk rises it can drop ca and vice versa.

 

Have you tested your newly mixed water and then the tank after a waterchange?

[Aurortpa]

Mag doesn’t get used as much as cal or alk by livestock...the export of it is actually very slow, as slow as it is to try to import.  That’s why you typically have to dump a lot in a system to raise mag.  I keep my mag with no problem around 1400 so I wouldn’t be concerned.  In a nut shell, one of the main functions of mag is to help you not lose alk or cal because of precipitation, so it does have a role for cal but isn’t interdependent on it.

 

[NanoRox]

I think this will be my coarse of action:  I may be wrong but my perception of having to change from a kalk set-up to 2 part dose is not worth the effort for this.  I know how much Ca my tank is using on a daily/weekly basis so I am going to manually dose Red Sea Part A to get my ca where I want it.  Then, I will put the needed amount in my ATO based on a weeks avg. need (since my ATO has to be refilled every 7 to 10 days).   I wont change anything else.   

 

Thanks for the feedback and info everyone. 

[NanoRox]

20 hours ago, Clown79 said:

Mag is just fine. It's not high. I've had mine at 1500. 

Mag being low is an issue.

 

Ca is a tad low. Should be 380-450

 

Alk is fine.

 

I

Using 2 part dosers is far easier as you dose according to alk consumption and equal part of ca.

 

This keeps them balanced because as alk rises it can drop ca and vice versa.

 

Have you tested your newly mixed water and then the tank after a waterchange? 

well there is the rub...don't judge but I am attempting to NOT make any water changes (2 1/2 months so far and tank has never been better).  I know the water changes would add Ca back and all the other benefits (if needed) but for me it messes up my tank balance I have established.  My nutrient export is working flawlessly and my import has been fine until this Ca dip.  Rather than to toss the baby out with the tank water, I am just going to adjust my Ca dosing and make water changes only in case of dire need.   Thanks so much for the input.  It helped me decide what to do. 

[Aurortpa]

How did this work out?

 

I am also trying to reduce my water changes, 10% weekly vs 25%...idk about a couple months tho!  I figured I need to “wean” my system tho till it can adapt.

 

I just got to the tail end of my nuisance algae waning, so I’m taking any maintenance changes very slowly as a precaution. Curious what your experience has been and why you think that it’s working for you.  If you’ve written about this, please point to the thread.

[NanoRox]

Like a charm.  I purchased the Red Sea Ca  and dosed and instructed to get my Ca back up to the 460 range.  Then, based on my the tanks daily Ca usage I calculated out that I needed to add 4 ml of the Ca to my ATO water.  been good ever since.

 

Regarding the water changes, I am approaching 3 months now and the tank has never been better.  I approach it this way - water changes serve a purpose of either aiding in nutrient or pollutant export or nutrient/trace element import with my primary goal of maintaining sustainable parameters.  I was not able to maintain my parameters consistently when I was making so many water changes.  I had to export nutrients when I first started so I had no choice BUT once my Chaeto reactor was able to handle that, my need to change the water decreased substantially.  I also chose to use Kalk in my ATO and have since decided to add all my dosing elements to the ATO (except occasional sodium bicarb).  My evaporation rate has been very consistent so I have calculated out the needed doses of the various elements and then just let it go.  My parameters have been rock solid, I have no algae and coral growth has been great.  So unless something happens that will require a water change, I don't see the need.  This latest Ca question was my latest learning curve in knowing how I should approach it.  

 

The weak link in this system, however, is if the evaporation rate and thus rate of refill/dose drastically change.  So far over the last 3+ months it has been stable with just a small variance up or down so it has not been a problem.