Does calcium drop automatically with the addition of bicarbonate?

[Cory]

Just want to know this. Or does it drop only when one is really high?

 

[Cory]

Oh man I don't know how to edit the title. It should say "Does calcium drop automatically with the addition of bicarbonate?"

 

[Randy Holmes-Farley]

It does not drop automatically.

It drops only when corals and other organisms use it to make calcium carbonate skeletons, or there is some abiotic (nonbiological) precipitation of calcium carbonate on things like heaters and pumps.

 

[Cory]

Yes I thought so. But from one of your articles, you have graphs, and there is a square in the middle. You said something on the lines of, "pushing the limits of either calclium or bicarbonate may result in one lowering the other". Again that's from my memory haha.

So if I add calcium chloride to boost calcium from 380ppm to 420ppm my alkalinity will remain the same? If I've got 2.5meq/l it should stay the same with a calcium boost? But if I had very high alk adding more bicarbonate would lower the calcium because it would combine with calcium to make sand right?

 

[Randy Holmes-Farley]

Pushing either one too high will accelerate abiotic precipition, but how much that happens depends on other things too, such as pH and magnesium.

With the calcium boost you suggest , alk won't change.

 

[Cory]

What is it that's ultimately deciding on general change in seawater, ph? For example in the body it's probably how fast or slow you breathe. That changes gas concentration. Sorry if I give you any headaches.

 

[Randy Holmes-Farley]

The ultimate deciding factors on precipitation are the concentrations of carbonate (which depends on alk and pH) and of calcium.

A pH rise of 0.3 pH units about doubles carbonate, so it is a big factor.

Magnesium is a kinetic factor, not a thermodynamic one, so its effect is not so easily calculated.

 

[Cory]

what would you worry about when adding baking soda? And calcium?

If I kept adding bicarbonate but no calcium wouldn't it eventually deplete all the calcium? For example in a beaker of seawater.

 

[Randy Holmes-Farley]

Yes, that would happen. Alk would get very high and calcium would drop.

If you are adding both, however, that won't happen,

 

[s2nhle]

Wow, thank you very much for sharing your knowledge. I have learned alot from these conversation.

 

[Randy Holmes-Farley]

You're welcome.

Happy Reefing.

 

[Cory]

Yes, that would happen. Alk would get very high and calcium would drop.

If you are adding both, however, that won't happen,

I too am learning a lot. Randy has some great articles, but after reading I got some launguage doubts.

What is the point at which it will precipitate lowering calcium? 14dkh? Why would that beaker of seawater deplete calcium but not if both are added? I guess just because it's the recipie for sand?

 

[Randy Holmes-Farley]

There is no specific point where precipitation takes off.

Seawater at pH 8.2, alk 7 dKH and calcium 420 ppm is already over the saturation point, so precipitation may happen very slowly. Temperature accelerates it, which is why heaters and pumps get coated.

As any of these rise, the potential for precipitation gets higher and higher.

At 14 dKH, I'd expect the precipitation to be fairly slow. At double that level the precipitation will accelerate greatly.

 

[Cory]

Ok thanks. Can you help me understand in simple terms what saturation point means? how is it saturated? Natural law? Like dissolved to the max?

I asked about alk causing calcium to drop if high, you said 28dkh would speed it greatly. What about the opposit situation, adding calcium chloride in a beaker of seawater. How much would cause it to drop?

 

[Randy Holmes-Farley]

Yes, dissolved to the max. Being supersaturated means that if you waited long enough, calcium carbonate would precipitate from seawater.

Yes, adding a lot of calcium to seawater will precipitate calcium carbonate. So will raising just the pH.

 

[Cory]

But in order to raise the ph you must raise one part of alkalinity, right? Bicarbonate, strontium, hydroxide, etcetera.

 

[Randy Holmes-Farley]

Or you can strip out CO2.

 

[Cory]

So photosynthesis is the deciding factor in reefs causing mainly a drop in cal and alk? One time my chaeto exploded in growth and I couldn't figure the cause of my alk going from 7dkh to 5dkh, considering I had no live rock and no corals to use calcium. Do you suppose the ph could have gotten high enough to do that?

 

[Randy Holmes-Farley]

Maybe.

Many corals also calcify faster at higher pH.

 

[Cory]

I'm not understanding ph completely. What sort of mental image would help understand ph? tiny balls of energy moving faster as ph rises and getting slower as ph lowers or?