Article on the degradation of limewater

[randy holmes-farley]

My article on the degradation of limewater has posted at:

http://reefkeeping.com/issues/2003-05/r ... /index.htm

In it I conclude that folks are overly concerned about degradation by carbon dioxide.

 

[Robin Goodfellow]

Consequently, the dosing of limewater from such large still reservoirs can be just as effective as dosing using any other scheme, and may have substantial advantages. These advantages include simplicity of the system and the ability to use organic acids such as vinegar to boost the potency.

hi.
I agree with your conclusion. However, I wonder why vinegar can not be used in a kalk reactor? It is simply dosing the RO/DI with vinegar before entering the reactor, right? For example, if the kalkreactor is on a timer, we can dose the vinegar via a metering pump on a specific interval if the vinegar solution has to be prepared on demand.

 

[randy holmes-farley]

. However, I wonder why vinegar can not be used in a kalk reactor?

There is no scientific reason not to, it is just a substantial engineering challenge that cannot be readily accomplished without significant modifications and complications.

 

[Syris]

Randy,

I built and have been using a Nilsen reactor for several weeks now. My problem is saturated Kalk is said to be a PH of 12+. When I charge my nilsen reactor by adding new additions of Kalk powder (~6 tblsp) the output measures a PH of 12+ but quickly drops over a couple days to a PH of ~10 even though there is plenty of undissolved Kalk powder in the reactor. A small powerhead attached to the reactor runs 6x a day for 15 min each to mix the solution periodicaly. This reactor is fed by a small powerhead in a resevoir of RO water controlled by a float switch in my sump.
Is this drop in PH a result of carbon dioxide absorption? Or a bad Kalk powder mix? I know you say that PH is less usefull measurement of the potency of saturated Kalk but it is the only means available to me. I use Kent Kalk, but have bought but not tried ESV brand. Can Kalk powder mixes if improperly stored absorb carbon dioxide faster than a saturated kalk?

Thanks for any insight you can provide.

 

[randy holmes-farley]

What kind of water is feeding the reactor?

 

[Syris]

I use well water run thru a TapWater Purifier. Well water PH is 8

 

[randy holmes-farley]

If the well water has a fair amount of CO2/bicarbonate/carbonate in it, that might be causing the formation of CaCO3 more rapidly than usual.

Ever measure it for alkalinity?

 

[Syris]

I will measure my well water for alkalinity tonight and see.
what is considered a bad reading for it?

 

[randy holmes-farley]

For normal use (like top off), there's no problem, but for sending it into a Nilsen reactor, perhaps any measurable value could be a problem. I've never tried it myself, but you'd be delivering the materials to precipitate CaCO3, which might coat the lime particles present.

 

[Syris]

Measured my PH in the kalk reactor again its now 9.4 with plenty of sediment on the bottom. I then stirred it manually and it was 9.5 not much different. I then emptied it and refilled with ESV kalk powder this time (6tblsp) PH 12.6. I will see in a couple days if it start to drop again.

As for well water PH was 8.6 and Alk was 5.8 dKH. I have not measured after I run it thru the Tap Water Purifier. Would it be any different?

What does all this mean? Will a Nilsen reactor not work for me in my situation? Would a real RO/DI unit be better? Time for a CO2 Calcium reactor instead? 8O
Sorry for all the questions this one just has me stumped and I can't keep my Alk and Ca up there. I dose B-Ionic too but my readings are dropping from 9.9 dKH to 7.8 and Ca of 400 to 350. I don't want to have to rely on B-Ionic alone.

TIA

 

[randy holmes-farley]

IMO, you'd need to purify that water before using it in a Nilsen reactor. I think that a lot of the calcium hydroxide is being destroyed in the reactor, making useless calcium carbonate.

A TWP would work, but might get expensive. Any type of RO or RO/DI would also likely work.

 

[Robin Goodfellow]

hi.
TWP is DI, and as far as impurity goes, RO/DI is not going to do it any better, except that it will be cheaper to run because of the extra RO.

I did not give much thought into rather dissolved CO2 can pass thru RO membrane (it is about twice as big as H2O, but then many things go thru)... or being ionic, it will be absorbed by the DI resin... Any idea?

The only way to degas CO2 out of water that I know of is to boil it... or to let it goes "flat."

 

[Syris]

My Kalk reactor water is a PH 12.4 not much different than last night when I made the new batch but its only been 24hrs.

Would airating my well water with an air pump before sending thru the Kalk reactor help?

BTW don't mean to hijack you're thread Randy with my problem. I liked the article a lot and made me think about my Kalk problem.

 

[randy holmes-farley]

No problem on the thread.

Since you actually have bicarbonate rather than CO2 in that well water (based on the pH and alkalinity), I think it will be hard to "degas" it by aeration.

 

[Robin Goodfellow]

hi.
either RO and DI can get rid of the bicarbonate in the water, right?

 

[Anonymous]

http://www.aquaticreefsystems.com/Rever ... ection.htm

RO gets rid of ~95% according to the link above.

bicarbonate in water is an ion then the DI would get rid of all of it basically.

But don't take my word for it. Randy has forgotten more chemistry then I have ever known.

 

[-JB]

Interesting, I'm using a nilsen reactor as well. I put about 1 1/2 cups of ESV Kalk in it every three weeks. The spin bar goes on for 5 minutes every three hours. I notice that the pH which starts of around 12.4 goes to around 11.5 within a week. Same thing, there is plenty of kalk in the reactor and the pH still measures mid 11. I use RO/DI water to feed the reactor and my water is stored in a 35 gallon Rubbermaid container that is aerated.

 

[Robin Goodfellow]

hi.
JDM, you pretty much said what I expected, but let's wait for Randy's comment.

For those that encounter lowered pH even when there are kalk in the reactor, did you add fresh kalk to the reactor to see if the pH will climb back up? I ask because it is not very easy to tell active kalk from dead carbonate, at least when I look at it. So the excess kalk you see in the bottom can be all carbonate, and does not make the solution saturated (hence, lowered pH).

 

[randy holmes-farley]

JB:

Why do you aerate the water? Have you ever tried not doing so? Maybe it will be CO2 deficient if unstirred, and might deplete the lime less???

bicarbonate in water is an ion then the DI would get rid of all of it basically.


either RO and DI can get rid of the bicarbonate in the water, right?


Yes.

CO2 (not bicarbonate) can get through an RO, but it usually gets caught in a DI and that is why RO/DI users with high CO2 well water sometimes try to degas the water before the RO/DI: so as to make the resins last longer. But with a pH over 8, there is little CO2 and lots of bicarbonate in the water in question (assuming that the alkalinity is not coming from phosphate or something even more unusual).

So the excess kalk you see in the bottom can be all carbonate, and does not make the solution saturated (hence, lowered pH).

Quite right!

 

[-JB]

I aerated the water because I had read that pure RO/DI water, for so reason or another should be aerated. It was from Anthony Calfo. But I can't for the life of me remember exactly why right now. Something about the water not being buffered and the airstone would help out. Do you think I should ditch the airstone?