What's making my alk rise

[LxHowler]

So I have an issue that i can't seem to find a solution to online anywhere. Over the past few weeks my alk has slowly been rising. I run my mixed reef normally at 9 dkh but over the past weeks it has slowly been creeping up, currently 9.6 confined by a Hannah checkers and a salifert test. I am not dosing anything at the minute and am doing 10% water changes weekly. My salt mix mixes to around 8.6 but even the water changes don't seem to bring it down. Anybody have any ideas what could cause this?
Tank parameters
Ammonia 0
Nitrite 0
Nitrate 10
pH 8
Dkh 9.6
Calcium 400
Magnisium 1300
100 liter mixed reef mostly frags at the minute

 

[myinvalidname]

I’d double check the salt mix. Most have dkh values of 10+. And the ones around 8.5 dkh have calcium concentrations of 450 and 540 ppm.

 

[blasterman]

I've had reef Crystals test 13dkh out of the bag. Coralife (only used it because somebody gave it to me) as high as 14.5dKH.

Otherwise, the only variable that can cause dKH to arbitrarily rise is if something is rapidly using calcium.

 

[LxHowler]

I’d double check the salt mix. Most have dkh values of 10+. And the ones around 8.5 dkh have calcium concentrations of 450 and 540 ppm.

This is what's confusing me, salt mix mixes higher calcium but it is dropping where it is being used by the coral but my dkh is still rising?

 

[LxHowler]

I've had reef Crystals test 13dkh out of the bag. Coralife (only used it because somebody gave it to me) as high as 14.5dKH.

Otherwise, the only variable that can cause dKH to arbitrarily rise is if something is rapidly using calcium.

Does this mean that adding new coral could in theory make my dkh rise as I have recently added a few new corals

 

[myinvalidname]

Does this mean that adding new coral could in theory make my dkh rise as I have recently added a few new corals

Corals use both calcium and carbonate (alkalinity) to grow. So no.

I’d double check the salt mix... double check your alk test kit (or your Ca). Is there anyway you have something like a non-calcium carbonate salt in the top off water?