Reef Chemistry Question of the Day #210 Limewater/Kalkwasser Long Term Use

[Sabellafella]

And other uses of carbonates beyond calcification that don't involve Ca. Randy makes all of this quite clear in his well written articles.

Heres your answer
"You have adjusted the concentration of dry solid calcium hydroxide added to the freshwater so that the aquarium maintains an alkalinity of 8 dKH as measured with a Salifert test kit."

 

[Crashjack]

A and D. Corals uptake a small amount of strontium when they take in calcium. Therefore calcium and alkalinity aren't actually used up equally... say 99% calcium, 1% strontium, against 100% alkalinity. Magnesium is utilized keeping calcium in solution. Since no magnesium is added but it is used, magnesium levels decrease over time.

I read this in some of Randy's articles a few months ago, but I probably didn't explain exactly right.

 

[rushbattle]

A & D for sure. Curious about the E/F thing. Is hydroxide alkalinity significant?

He just threw those options in to throw you off. Hydroxides interact with dissolved CO2 to make carbonates almost immediately after addition to actively mixed seawater. No buildup possible unless you have no dissolved CO2, almost impossible and would indicate zero gas exchange.

 

[rushbattle]

Heres your answer
"You have adjusted the concentration of dry solid calcium hydroxide added to the freshwater so that the aquarium maintains an alkalinity of 8 dKH as measured with a Salifert test kit."

Yup, so Ca rises because you are maintaining steady alk.

 

[GQuinn]

Lot of speculating. What is the real answer?

 

[salty joe]

I'm going with D. Just D. The rest either seems iffy or is wrong. IDK.

Come on Randy, how long are you gonna leave us twisting in the wind?

 

[Orm Embar]

You shoud read about one of the reasons why Randy prefered basic Instant Ocean for his salt.

Dagnabit, I hate being wrong! . . . OK, I am changing my answer to A & D. My followup questions: why does this happen, and how do you deal with the fact that calcium will climb long term? Do you periodically dose sodium carbonate, rely on partial water changes, or just ignore the calcium level?

 

[Shon]

Reef Chemistry Question of the Day #210

Suppose that you have a coral reef aquarium where you dose limewater (kalkwasser) daily to replace most of the evaporated water. You have adjusted the concentration of dry solid calcium hydroxide added to the freshwater so that the aquarium maintains an alkalinity of 8 dKH as measured with a Salifert test kit.

You experience a daily pH range from 8.0 to 8.2, and you perform no water changes and use no other additives.

Which of the following will likely happen long term (weeks to months)? List all that apply.

A. Calcium will slowly rise
B. Calcium will slowly fall
C. Magnesium will slowly rise
D. Magnesium will slowly fall
E. The true carbonate alkalinity will slowly decline as it is replaced by hydroxide alkalinity
F. The true carbonate alkalinity remains unchanged but the total alkalinity increases due to accumulation of hydroxide


Good luck!













.

Im a noob but I'll take a shot at it..

- Ph swings (daily) So co2 plays a role? Doesn't that help replace carbonates? So not F..
-Maybe E, I havent learned that much yet but wouldn't it break down/bond to another element(s)?
-D for sure (I hope), Mg is used but not replaced, like Iodine, Iron and other elements.
-C, opposite of D, No
-B, Only if it is being used faster than it can be replaced. But I read somewhere that Mg plays a role in availibility so I guess you can have alot of it with concrete sand, jammed powerdheads and wave makers.. so yes?
-A.. yes? Just not in a form available/testable?

A,B,D and E?

Good thing I don't have a tank yet. Bring on the ed-mc-cation! I am still learning.

 

[Dizzirn]

Following

 

[Mjl714]

D and E.

 

[Mjl714]

You shoud read about one of the reasons why Randy prefered basic Instant Ocean for his salt.

Would you elaborate?

 

[jason2459]

Would you elaborate?

I believe I did above.

 

[Randy Holmes-Farley]

And the answer is...
A. Calcium will slowly rise
D. Magnesium will slowly fall

Limewater (kalkwasser) adds calcium and alkalinity in almost exactly in the ratio found in pure calcium carbonate. If there is magnesium present in the calcium hydroxide used to make the limewater, very, very little is able to dissolve into the high pH limewater, effectively increasing the purity of the calcium and hydroxide present.

When calcium carbonate preciptates in a reef aquarium, either by organisms making skeletons or through abiotic precipitation on pumps, there is some incorporation of magnesium in place of calcium in the calcium carbonate structure. Thus, the demand for calcium is a little less than what was supplied (assuming alkalinity is maintained), and the demand for magnesium is a little more.

Over time, when maintaining alkalinity, calcium rises and magnesium declines.

For this reason, in aquaria that rely strongly on limwater, using a lower calcium salt mix can be a good choice, and many such tanks may need some magneisum supplements if water changes are not enough to keep it at adequate levels (although some salt mixes start with excess levels of magnesium, and so it may stay elevated in those systems).

Nothing unusual happens with the alkalinity when using hydroxide to supplement it, so E and F are not correct.
When limewater is used in a reef tank, it quickly combines with atmospheric and in- tank CO2 and bicarbonate to form bicarbonate and carbonate:

OH- + CO2 → HCO3-

OH- + HCO3- → CO32- + H2O

Once in the tank at an acceptable pH, there is no concern that the alkalinity provided by limewater is any different than any carbonate alkalinity supplement. The hydroxide immediately disappears into the bicarbonate/carbonate system. In other words, the amount of hydroxide present in tank water is really only a function of pH (regardless of what has been added), and at any pH below 9, it is an insignificant factor in alkalinity tests (much less than 0.1 meq/L). Consequently, the fact that alkalinity is initially supplied as hydroxide in not to be viewed as problematic, except as it impacts pH.

 

[Shon]

Good to know, got to spend the next weeks morning coffees reading these.

 

[cvicente]

I missed that Chemistry class...

 

[Mjl714]

I believe I did above.

Thanks, opened my eyes, and saw link, good stuff.

 

[jason2459]

Past reply from Randy which I will copy paste into threads asking for what's the "best" saltmix and what I was referring to

"I do not think there is a "best" salt mix. Nearly all of them will work fine as long as you know their pros and cons.

I personally prefer Instant Ocean, and this is why:

I don't want excessive borate, which leaves out Seachem.

I don't want vitamins or anything else organic in my mix, so that tosses out some like Reef Crystals, hW Marinemix Plus BioElements, Kent, Coralife, and Nutri-SeaWater.

I don't want excessive calcium (long term use of limewater as I use drives up calcium, so I do not want it starting high), so that tosses out a bunch, such as Kent, Seachem, Coralife and Oceanic.

There are certain companies that I will not support due to their misleading claims and/or product lines. That tosses out a few which I won't detail here since it is my personal thought as opposed to a specific issue with their salt mix.

I won't use certain lines of natural seawater due to excessive metals in it.

That only leaves a few to choose from, such as Instant Ocean and Tropic Marin Pro. The remaining ones might all be fine for me, but IO is lower in cost, especially if you get it when it goes on sale (which it frequently does)."

 

[Orm Embar]

Randy - thanks for the explanation! How do you deal with the rising calcium? Just use alkalinity replacement and wait for the calcium to naturally drop, rely on partial water changes to maintain an equilibrium, or something else?

 

[CindyKz]

A

Nothing unusual happens with the alkalinity when using hydroxide to supplement it, so E and F are not correct.
When limewater is used in a reef tank, it quickly combines with atmospheric and in- tank CO2 and bicarbonate to form bicarbonate and carbonate:

OH- + CO2 → HCO3-

OH- + HCO3- → CO32- + H2O

Once in the tank at an acceptable pH, there is no concern that the alkalinity provided by limewater is any different than any carbonate alkalinity supplement. The hydroxide immediately disappears into the bicarbonate/carbonate system. In other words, the amount of hydroxide present in tank water is really only a function of pH (regardless of what has been added), and at any pH below 9, it is an insignificant factor in alkalinity tests (much less than 0.1 meq/L). Consequently, the fact that alkalinity is initially supplied as hydroxide in not to be viewed as problematic, except as it impacts pH.

I hate when I know something, but I forget that I know it, until I get it wrong.

Thank you once again Randy!

 

[reef life]

Randy's Forum is one of my go to forums to read. Always great info!