Alkalinity vs calcium stability question

[Sophie"s mom]

So we know that ALK and Calcium move in opposite directions, so my question is, if I keep alk stable with minor dosing, will calcium stay stable as well? I know this may be a dumb question, but I am honestly curious because When I have had to dose alk, it is very minimal and my calcium so far has remained 425. So if 1 is stable, will the other automatically be stable as well?

 

[Gumbies R Us]

I've seen some people who will have high alk, low calcium, and vice versa. I'm in a boat similar to yours. I'm on the lower end with alk but around 440 for my calcium

 

[Sophie"s mom]

I've seen some people who will have high alk, low calcium, and vice versa. I'm in a boat similar to yours. I'm on the lower end with alk but around 440 for my calcium

I do know that they move in opposite directions, meaning if ALK goes high, calcium will lower, and vise versa. SO that just got me thinking if one remains stable, does that mean the other will follow suit?

 

[Randy Holmes-Farley Verified Community Expert]

So we know that ALK and Calcium move in opposite directions, so my question is, if I keep alk stable with minor dosing, will calcium stay stable as well? I know this may be a dumb question, but I am honestly curious because When I have had to dose alk, it is very minimal and my calcium so far has remained 425. So if 1 is stable, will the other automatically be stable as well?

Well, I don't agree with the generality that they move in opposite directions. That's an excessive oversimplification. If I add both, both rise. if I consume both, both decline. . if I add just one, nothing immediately happens to the other.

It is true that if both are being used, and you add just one, the other necessarily declines.

 

[Randy Holmes-Farley Verified Community Expert]

I do know that they move in opposite directions, meaning if ALK goes high, calcium will lower, and vise versa. SO that just got me thinking if one remains stable, does that mean the other will follow suit?

No, and no.

Adding both at the amount they are consume will lead to stability of both. Stabilizing alk does nothing to stabilize calcium.

 

[Reeferbadness]

I also scratch my head on this topic, even after reading many articles stating more or less what you said. I have a 4 head RS doser and a Trident so i can get tests multiple times a day and adjust Alk/Cal/Mag as needed (from anywhere - the RS doser app is cloud based). I'm actually kind of obsessed with the readings and make small adjustments often. Swings in either seem to be more random and sometimes happen together. I have achieved a very nice stability but still don't really understand exactly how the take up from the corals (and corraline algae) effects the ratios.

 

[Sophie"s mom]

No, and no.

Adding both at the amount they are consume will lead to stability of both. Stabilizing alk does nothing to stabilize calcium.

Perfect, thank you Randy, that is exactly what I was looking for.

 

[Randy Holmes-Farley Verified Community Expert]

I have achieved a very nice stability but still don't really understand exactly how the take up from the corals (and corraline algae) effects the ratios.

All corals and coralline algae use about 18-20 ppm calcium and 0-1 ppm magnesium for each 2.8 dKH of alk consumed.

There are some other, typically quite minor, processes that consume or add alk, and water changes can mess with the demand ratio. Rising, falling or dosing nitrate or some forms of ammonia, and sulfur denitrators are the biggest of these minor deviations from that fixed ratio.

This has a lot more:

When Do Calcium and Alkalinity Demand Not Exactly Balance? by Randy Holmes-Farley

 

[Reeferbadness]

All corals and coralline algae use about 18-20 ppm calcium and 0-1 ppm magnesium for each 2.8 dKH of alk consumed.

There are some other, typically quite minor, processes that consume or add alk, and water changes can mess with the demand ratio. Rising, falling or dosing nitrate or some forms of ammonia, and sulfur denitrators are the biggest of these minor deviations from that fixed ratio.

This has a lot more:

When Do Calcium and Alkalinity Demand Not Exactly Balance? by Randy Holmes-Farley

Thanks Randy! Your input is always appreciated and very helpful

 

[Randy Holmes-Farley Verified Community Expert]

Thanks Randy! Your input is always appreciated and very helpful

You're welcome.

Happy Reefing.