is my kalkwasser saturated?

[jayo]

I don't know how to measure this well. Searching this forum it seems that I should be able to dissolve about 1.5 to 2 tsp of CaOH per gallon fresh water. This surprised me, because even if I add less than a teaspoon/gal the solution is very cloudy and solids will settle to the bottom of the container.

Do I just need to mix longer? How long should I be mixing?

thanks,
jayo

[OUinLA]

Solids should settle on the bottom as far as I know. Mine is always cloudy too, but when dripped in the tank it doesn't cloud the water.

[Randy Holmes-Farley]

It usually does not "completely" dissolve because there are things in it (like magnesium hydroxide) and things that form on mixing with water in air (calcium carbonate) that will stay as solids.

Just let most of the solids settle and then use it.


Here's an article that describes the stability of limewater on exposure to air:

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

[jayo]

that's a great article, after I read it I started mixing 20 gal of kalk at a time to dose in over a week.

My concern now is making sure I start with a saturated solution because my calcium and alk tend to drop over time.

So I should just add 2 tsp CaOH/gal, mix it for a couple minutes, and assume it is saturated?

My limewater is clear after about an hour or so of settling, but I get a lot of solids on the bottom. Oh well.

jayo

[Randy Holmes-Farley]

There is nothing wrong with adding more solids, and just leaving the solids on the bottom. That will help ensure that it is saturated. It might also help purify the water more, as described in this article:

The Self Purification of Limewater (Kalkwasser)
http://www.advancedaquarist.com/issues/may2003/chem.htm

[simonh]

IIRC solubility is something like 1.6grams per litre at 20C. Slightly more at lower temperatures. It will also depend slightly on the purity of the calcium hydroxide and things like amount of CO2 in the water.

So, I add 2grams per litre in my 75litre covered top off container. Mix vigorously with a powerhead for 5 minutes. Then leave it to settle. Dose over the week. Refill and repeat as necessary. Works great.

[andy-hipkiss]

Possibly total trivia but with excess Ca(OH)2 but no mixing in a ~35 l container, a limewater of approx pH 10 was achieved. Not a hugely useful observation but I forgot to plug in my mixing pump a week or so ago. Since I was recalibrating my pH probes last night I thought it would be interesting to see what was happening in the "kalk bucket".

Damn, I lead an exciting life :D

[AcroSteve]

Originally posted by Randy Holmes-Farley
There is nothing wrong with adding more solids, and just leaving the solids on the bottom. That will help ensure that it is saturated. It might also help purify the water more, as described in this article:

The Self Purification of Limewater (Kalkwasser)
http://www.advancedaquarist.com/issues/may2003/chem.htm

That is what I have been doing, But I have wondered if I should ever get rid of the left-over solids?

I have not measured accurately and do not know how much "good" stuff is left in the bottom. Last time, I just dumped 1/2lb of balls in and add water to it occasionally. I have not been keeping a log on my kalk tank.

Will measuring the PH of the solution give a good indicator of the concentration of the solution?

[Randy Holmes-Farley]

But I have wondered if I should ever get rid of the left-over solids?

I was the container out about once a year, but some folks might build up solids faster than I do.

Will measuring the PH of the solution give a good indicator of the concentration of the solution?

A rough measure, if you do it carefully. Put 2 teaspoons of lime in a cup of DI water and stir for a minute or two. Then use that as the pH standard. Compare the bulk limewater tank to that standard.


If there is no difference, it is about saturated. If the pH difference is 0.3 units, then the bulk limewater is about half saturated.

[Jimbo327]

So what is the average or typical pH range of saturated kalk water (when you put 2 teaspoon of lime in a cup of water)? I don't have any excess lime around. Thanks.

Jim

[Randy Holmes-Farley]

Saturated limewater willl have a pH in the mid 12's (about 12.4, IIRC; it depends on temperature), but do not rely on a pH meter calibrated at pH 7 and 10 to give an accurate measurement at this pH.

[simonh]

Listed in this document is the pH of saturated Calcium hydroxide at various temperature:

http://www.sigmaaldrich.com/Brands/Fluka___Riedel_Home/Bioscience/BioChemika_Ultra/Biological_Buffers.html

As can be seen it has a very high temperature dependence. In my garage at this time of the year (10C) it has a pH more like 13, whereas in the summer it may be only 12.45. But, as Randy said knowing the exact theoretical pH isn't that much use given that a hobbyiest calibrated meter is unlikely to measure such extremes very well.

[ejmeier]

Don't mean to steal this thead, but I am getting mixed signals over just how much lime to add to water to make full strength kalk. I don't know if it is confusion over abbreviations or what, so I will spell everything out.

Searching this forum it seems that I should be able to dissolve about 1.5 to 2 tsp of CaOH per gallon fresh water.

I did a search as well, and came up with nothing. But TSP = TEASPOON. So is it 2 TEASPOONS to saturate kalk, or TABLESPOONS. I also read in a book by Ron Shimek that it is actually 2 TABLESPOONS (TBSP) to saturate kalk.

So, let's see, 3 TEASPOONS in a TABLESPOON would be 6 TEASPOONS according to Dr. Ron. Either jayo is mixing kalk at 1/3 saturation, or I am mixing it at 3x what I need to be. Who is right?

[simonh]

Around 1.5grams of calcium hydroxide will dissolve in 1 litre of pure water at 25C. Water at 0C will dissolve around 1.8grams per litre.

I therefore use approx 2grams per litre to allow for varying water temperature in my garage and also formation of calcium carbonate due to CO2 in the water or other precipitates due to impurities in the Ca(OH)2. So, 1 gallon would be around 7.5grams of calcium hydroxide to produce a saturated solution.

I'm no good at cooking so not quite sure how much 1teaspoon vs 1tblspoon full weighs.

[ejmeier]

Originally posted by simonh
So, 1 gallon would be around 7.5grams of calcium hydroxide to produce a saturated solution.

I'm no good at cooking so not quite sure how much 1teaspoon vs 1tblspoon full weighs.
I'm not 100% sure either, but one tablespoon equals 4 fluid grams. I don't know what the difference is between regular grams and fluid grams, if there is any. But that would work out to about 1.875 tablespoons or 5.625 teaspoons needed to saturate water.

That's too many "spoons" if you ask me.;)

[Randy Holmes-Farley]

There are additional complications as well. For example, I use calcium oxide (quicklime), not calcium hydroxide (lime). The calcium oxide is 32% more potent than calcium hydroxide (by weight)

At 25 deg C, you can dissolve 0.0204 moles of either in 1 L of water. That's 1.14 grams of calcium oxide and 1.51 grams of calcium hydroxide per L (4.3 and 5.7 grams per gallon).

A teaspoon holds 4.93 g of water.

A tablespoon holds 14.79 grams of water.

These solids are more dense than water, but are also puffy because there is air in between the solid particles. How much air depends on how the solid is made, etc.

In the end, a teaspoon of these solids weighs a few grams. That's why folks say it takes 2 teaspoons per gallon. It is a crude measure that varies from lot to lot. It should not take 2 tablespoons to saturate a gallon, but there is no problem adding that much and letting the remainder sit on the bottom.

one tablespoon equals 4 fluid grams.

I don't know what a "fluid gram" is, but if that is true, it bears no relation to "grams". :D

[simonh]

I found that 1teaspoon = 5ml, 1 tablespoon = 15ml. 5ml of CaOH(2) weighs around 3grams. So a couple of teaspoons seems more reasonable.

Edit: Too slow on the keys today :)

[Randy Holmes-Farley]

And don't give me Habib's line about your answer having been submitted first because your answer had to travel farther to the server. :lol:

[ejmeier]

So about two teaspoons you say?

This would explain why I have about 2 inches of junk at the bottom of my reservoir after only about a month and a half...

Since there is so much stuff at the bottom of my reservoir from my previous overdoses, do you think that I can get by with filling the reservoir a few times without adding any pickling lime, or a greatly reduced amount?

BTW - thanks for all the help!:)

[Randy Holmes-Farley]

Since there is so much stuff at the bottom of my reservoir from my previous overdoses, do you think that I can get by with filling the reservoir a few times without adding any pickling lime, or a greatly reduced amount?

Yes, I've done that before. After a while, however, unless you have a way to measure the concentration in the water, you won't be able to know if it is still saturated or not, because some of the solids will be things that won't dissolve.

[simonh]

If you don't have a conductivity meter to measure the concentration then a calcium test kit may work quite well. I have used the Salifert calcium test kit with success for measuring the concentration of limewater. It would probably be best to use Randy's suggestion and make up a saturated solution, let that settle, and then take a measurement to use as a base line (somewhere around 800ppm or more). You should then be able to test your resovoir to know when you have used up all the disolvable solids.

Here is a post in the Salifert forum about the calcium test kit and limewater: http://archive.reefcentral.com/forums/showthread.php?s=&threadid=236190