Reef Chemistry Question of the Day #4

[Randy Holmes-Farley]

Reef Chemistry Question of the Day #4

When supplementing calcium and alkalinity with a two part (or three part) additive system, salinity necessarily rises over time, which it does not do when using limewater (kalkwasser) or a calcium carbonate/carbon dioxide reactor.

Why is that?

There was just a thread a few days ago on this topic, so count yourself lucky if you read that one.

 

[redfishbluefish]

Wow, 47 views and not a single answer. Here's a hint....the two parts you are adding are:


CaCl2......+.......Na2CO3** --------->
Calcium...................Alkalinity




** could also be NaHCO3

 

[Tphill]

I see NaCl in there.

 

[franciscosalazar]

NaCl reaction as 2 part is supplemented unlike limewater...

 

[GHill762]

can you provide a link to that thread? I'd like to read it and I can't seem to find it..

 

[DRThompson]

For 2 part:
Ca(Cl)2 (calcium additive) + Na2CO3 (alkalinity additive) + H2O ----->> CaCO3 (skeletal structure of hard corals) + NaCl (salt) + H2O
This would lead to an increase in salinity/salt (NaCl) over time.

For Kalk
Since there is no sodium or chloride in Kalkwasser Ca(OH)2 there would be no direct effect on salinity

 

[Crna]

Very interesting thread, thanks guys!!

 

[Keithcorals]

The two part is made with salts and kalkwasser is not

 

[Randy Holmes-Farley]

can you provide a link to that thread? I'd like to read it and I can't seem to find it..

I'll link it and copy the pertinent info here tomorrow.

 

[Randy Holmes-Farley]

can you provide a link to that thread? I'd like to read it and I can't seem to find it..

Actually, I guess I can post the link now, since folks who do not want to see the answer before they have a change to work it out for themselves don't need to follow it:

https://www.reef2reef.com/forums/reef-chemistry-randy-holmes-farley/172397-salinity-creep.html

 

[hart24601]

The ions! The ions!

 

[beaslbob]

Reef Chemistry Question of the Day #4

When supplementing calcium and alkalinity with a two part (or three part) additive system, salinity necessarily rises over time, which it does not do when using limewater (kalkwasser) or a calcium carbonate/carbon dioxide reactor.

Why is that?

There was just a thread a few days ago on this topic, so count yourself lucky if you read that one.

you add calcium chloride and sodium bicarbonate.

You get calcium, Carbonate and sodium chloride.

corals get calcium carbonate the sodium chloride increases salinity slowly

 

[Randy Holmes-Farley]

Great job. Many of you got this one exactly right!

Here's the blurb I wrote in the linked thread, explaining it:

Salinity definitely increases over time using a two part supplement.

It's not really due to impurities, but the way the method is designed.

The two main ingredients are sodium bicarbonate/carbonate and calcium chloride.

The corals use the calcium and carbonate to make calcium carbonate skeletons, but necessarily leave behind the sodium and chloride.

In a well designed two part, what remains is close in composition to seawater, so the ion ratios don't get messed with too much, but the salinity does rise.

Two good solutions are to replace salt water with fresh once in a while, or to do water changes with slightly lower salinity than the tank target value.