Alkalinity precipitation due to high calcium

[Hausser]

i am curious if any one know at what level does high calcium make ALK precipitate. My calcium is maxed out on my Red Sea test kit so I took to LFS and they tested and said my calcium is at 680.

This is a new set up tank and I am using coralife salt.

My parameters are
ALK 6.4
Calcium - maxed
Mag 1440

I have an 80 gallon tank with a 20 gallon sump. I did a 5 gallon water change 2 days ago and a 10 gallon water change yesterday usin IO salt mix. IO ( instant ocean) calcium tested at 375 calcium and ALK tested at 11. After water change and a few hours went by I tested my ALK and it never went above 7, calcium is still maxed out and mag is still 1440.

I am going to do another water change tomorrow and test. I does ALK and all it does is precip in the tank.

 

[Scott.h]

Wow.. have you been dosing cal? How much alk do you dose daily?

 

[Hausser]

I have not dosed anything, this tank has only been up and running 2 months. I have only 2 corals in it. I have dosed around 100ml of Red Sea alkalinity supplement but it keeps precipitating.

 

[Scott.h]

Since your lfs confirmed your test I'd have to think it would have something to do with your rock or substrate. What is it made out of? I've never experienced that. I would think if you couldn't dose enough alk, a big water change would correct it. Really weird. Curious as to what randy says.

 

[Hausser]

I have caribsea life rock and pink Fiji sand.

 

[Hausser]

So I tested my calcium again today after 15 gallon water change over last two days and still maxed. Took sample to LFS and they said calcium is down to 600. Did a 10 gallon water change today and tomorrow I will test and take sample to LFS and see if it is lower than 600. I did dose and still had precipitation but it was not as bad as when calcium was at 680.

 

[Triggreef]

What salt are you using? Some have very high Ca such as red sea coral pro. Could very well be your issue.

 

[Hausser]

I used coralife and know it has higher calcium.

 

[Scott.h]

Maybe do bigger water changes vs smaller. I'd still think calcium would precipitate when adding more alk. @Randy Holmes-Farley is this not the case?

 

[Randy Holmes-Farley Verified Community Expert]

I'd just let it fall on its own. Calcium is not the biggest driver of precipitation in the ranges we encounter in reefs.

620 ppm calcium is no worse for precipitation, relative to 420 ppm, than the pH rising from 7.8 to 8.0.

pH is the biggest driver, followed by alkalinity (since those can often double the supersaturation relative to normal seawater, but rarely does anyone attain 840 ppm calcium, which would be needed to double it).

 

[Hausser]

My biggest issue is when dosing alk it precipitates and looks like a snow storm in my tank.

 

[Randy Holmes-Farley Verified Community Expert]

My biggest issue is when dosing alk it precipitates and looks like a snow storm in my tank.

Some local precipitation of magnesium hydroxide is normal when dosing carbonate or hydroxide alk additives due to the high pH at the point of addition. It will redissolve on mixing.

If, in fact, you were getting calcium carbonate precipitation (slower, but it won't redissolve), then you can dilute it more, switch to bicarbonate additives (like baking soda), add to a higher flow area, and add it more slowly.

 

[Hausser]

Thanks for the help Randy

 

[Stigigemla]

The mathematics around precipation is very complex. You can say that Ca x kH causes precipation. Mg makes them more soluble. The temperature is also important.
Around the magnets in the pumps it is often a little bit warmer so many times it is the first place to find precipation. Thats why many people recommend to clean the pumps in vinegar a few times a year. And of course after visible precipation in the tank.