Testing for hardness

[Mazile]

The pool company tested my water and told me my TH was 180ppm. They said to add 8lb hardness-raiser to my 26,000 gal pool (I'm not sure exactly what compound it was, but it was recommended by Leslie's).

After adding the calcium compound, I tested for hardness. The instructions on the test kit say to add 5 drops of hardness indicator (a blue solution), and then the sample water should turn red "if there is hardness present." When I add the hardness indicator, the water does not turn red. It is a very pale beigy-sort of color. Having just added 8lb of hardness, it is hard to believe that there is no hardness present! (I do live in a very soft-water area, but this is ridiculous!)

After adding drops of the hardness titrant, the instruction tell me, the water should turn blue. No matter how many drops I add, the water never changes color -- not even a little.

I don't understand this. What is the problem? The test kit is brand-new.

I would sure appreciate some help w/ this. Leslie's has got me so tied up in knots, I don't know where to turn. [/u]

[tbenton]

I bought three Taylor reagents to test calcium hardness in our pool. I was told how many drops of each for each step of the test but did not tell me how to calculate the hardness based on third step. Can you/anyone tell me? Have had pool for a very long time but never tested for hardness before so I am at a loss as to how to calculate.

Step one - 20 drops of R-0010 calcium buffer
Step two - 5 drops of R-0011L calcium indicator
Step three - 'x' drops of R-0012 hardness reagent -until water turns blue

Thanks

Terri

[me_too]

That's correct. Option 1:

Use a 25 ml water sample, add 20 drops R-10, add 5 drops R-11L, add R-12 dropwise until water turns blue. Take your time adding R-12 dropwise watching for the color change after each drop, the endpoint is not as instantaneous nor as clear as the alcalinity test. The number of drops multiplied by 10 gives you the ppm count.

Option 2 (if you have any metals in the water they can interfere with the test):

Use a 25 ml water sample, add 20 drops R-10, add 2 drops R-12, add 5 drops R-11L, add R-12 dropwise until water turns blue. Take your time adding R-12 dropwise watching for the color change after each drop, the endpoint is not as instantaneous nor as clear as the alcalinity test. The (number of drops + 2) multiplied by 10 gives you the ppm count. You may get a clearer endpoint with this method.

I wouldn't worry about a TH of 180

[I am Johnny Tikinut]

Hello Everyone,

I recently purchased the TF-100 test kit. In testing the calcium hardness I followed the instructions as stated above and the water turned a pale and see through blue. Is the test complete immediately upon turning even the faintest blue? My previous test kit was a Leslie’s DPD test kit. I am new at maintaining my own pool, and I only used this kit to test chlorine, pH & alkalinity. With their alkalinity test the water changes from green to red. Generally the first drop that begins to make the color transition renders the solution pink. At this point one additional drop will reliably turn the solution red. With the TF-100 test for CH, after the solution turned pale blue I must have added 8 to 10 more drops of R-12 without any real discernable color change.

I apologize that I have not yet learned how to bracket the quotes correctly. I noticed that “me too” said: “Take your time adding R-12 dropwise watching for the color change after each drop, the endpoint is not as instantaneous nor as clear as the alkalinity test.” Is that what “me too” meant, that the end result is less dramatic (and lighter in color) than the alkalinity test?

I noticed that “me too” also described the method used for testing hardness in a pool with copper in the water. I don’t know that I have a test that specifically tests for copper, in fact I don’t see where the TF-100 tests metals at all. Do I need to take a sample to my local pool store to test for copper? In the meanwhile I suppose that I will just try testing using both methods and see if the results differ. If the results don’t differ can I then assume that I do not have a copper issue with my pool? Thank you in advance for any advice here. I really didn’t want to pester Dave and Meg of TF test kits, especially right now during the holidays.

[chem geek]

The CH test transition is more subtle than other tests such as TA. However, it does sound like the transition you are seeing towards blue that then doesn't change with more drops is the correct transition. The transition can be made sharper and not fade (change back with time) by initially adding some number of titrant drops to your sample first an then making sure to count those in the total. If you have metal in the water, then those initial titrant drops will react to remove interference from the metal ions. You can use this "add some titrant drops first" method even if there are no metals in the water -- the only downside is if you use too many drops and get an initially blue result instead of red when you add the indicator dye, but that would only happen if your CH level were very low.

Look at the demo for the Calcium Hardness test by looking at this link choosing "Pool/Spa" on the left, then the K-2006 kit "To Test Calcium Hardness" link, but add some titrant drops to the water sample before the 20 drops of calcium buffer.

[T3]

If you scroll down far enough at the bottom of the video demonstration page, there is a video demonstration of the modified calcium hardness test.

General Test Interferences:
Calcium Hardness Test [updated 3/10/10]

[Flora27]

normally it´s just a normal tiration. u take a definite volume of whater, let´s say 20.00ml add an idicator, and start adding EDTA drop by drop, until u see a permanent color change.