Taylor calcium hardness test

[carp6318]

I am using the calcium hardness test out of the taylor K2006C test kit and i keep getting the purple color instead of blue. I have added the five or six drops of titrant prior to the buffers as siggested but still get the same thing. I just do not trust the results I am getting and don't know if I should be doing something different. Stats for my pool in case they are needed are:

20,000 gallon salt pool
pool is 2-1/2 months old
FC 4.4
CC 0
Ph 7.6
TA 60
CH 460 (?)
CA 60
pool temp 66 degrees

[PoolDoc]

You've got a problem -- wierd test results -- but you may not need to 'solve' it.

I'm assuming your new pool is a plaster pool -- if not, repost and disregard some of what I'm about to say! -- and that your other readings are valid and normal.

Anyhow, given your readings, it's unlikely your calcium is too low. Taylor lists (on the page linked below) the following problems from HIGH calcium:

• cloudy water
• rough surfaces
• clogged filters and reduced circulation through piping
• heater inefficiency

But, there is usually LESS to these problems than all the pool industry warnings would suggest.

Cloudy water will normally occur, not gradually, but suddenly when you raise the pH or add some calcium chloride, calcium hypochlorite, or sodium bicarbonate. (When pool water turns cloudy gradually, it's more often a filtration or chlorination failure.) Don't do those things, and you're not likely to see calcium based cloudiness. And, if you DO need to raise the pH, if you'll use borax (as we usually recommend), a little at a time (as we usually recommend) you're not too likely to see a problem there. Your alkalinity is a little low, for a plaster pool. So, if you do add baking soda to raise it, just do so with small doses.

Filter problems from high calcium are often mentioned in pool industry literature, but I've never, ever encountered them . . . even when I TRIED to produce them. And, as best I can recall, I've never been able to get a reliable report of calcium based filter problems, here, either. So, maybe that problem has occurred, somewhere, sometime . . . but if so, it's pretty uncommon, and my suspicion is that some of those cases may be in places like Arizona, where they have really terrible fill water that contains OTHER minerals that can cause problems, like magnesium sulfate.

Rough surfaces, from minerals in the water, I have seen. But EITHER it was from other minerals (like they have in Arizona) OR it was from a combination of high pH, high calcium, and algae over the winter, in the absence of chlorine. However, simply lowering the calcium will NOT prevent that problem, though maintaining a pH below 7.6 over the winter probably will.

That leaves the issue with heaters. If you have a heater, then you are probably reasonable to worry about your calcium. Otherwise, you'll probably be fine if you (a) don't add more calcium, (b) maintain a lowish pH and TA, and 'keep an eye on it'.

On the assumption that you DO have a heater, let's keep going. High calcium with heaters IS a problem, and it is the ONE case where I've found the SI (Langlier Index) really matters. Over-saturated water WILL often result in calcium deposition in the heat exchanger and that will cause a loss of heater efficiency, or even damage to the heat exchanger. BUT . . . following the pool industry guidelines will NOT save you. The reason is that SI is very temperature dependent, and the SI that affects your HEATER is the one inside the heat exchanger, at temps of say, 110 - 130 degrees, and NOT the SI in your pool at say, 80 degrees!

Now, my personal experience has been, that commercial pools operated with a heater, but with pH of 7.3 - 7.6 and TA less than 100 ppm experienced minimal problems with CH levels > 400 ppm, even though that was seriously "over-saturated" water. But I don't know whether that experience is universally valid, or not.

So, IF you have a heater, it's probably worth figuring out what's up with the test. Otherwise, not so much.

The Taylor 2006C uses the Erichrome T indicator, I believe which gives you an indication of total calcum + magnesium. Taylor has some cautions about interferences, on this page
http://www.taylortechnologies.com/pr...asp?KitID=2233

Calcium, Magnesium, Total Hardness
Metal ions may cause interference; to prevent, add titrant containing EDTA to sample before buffer and indicator, then test as normal making sure to count drops of titrant added initially in total required to reach endpoint. If interference still occurs, dilute sample with DI water as necessary and retest.

Distilled -- distilled, NOT purified! -- water from the grocery store should be an adequate substitute for lab-grade DI (de-ionized) water. Just remember, if you dilute 50:50, you'll need to double your CH readings; if you dilure 75:25, you'll need to quadruple your endpoint reading.

Since you've already tried adding the EDTA first, I'd try the distilled water adjustment next, and see if you can get a consistent endpoint that way. I'd still add a couple of drops of EDTA first, through. You also might want to add the EDTA, swirl, wait a minute, swirl again, and then wait another minute before adding the indicator.

More info below!

Ben / PoolDoc



Here are the Taylor test instructions, from their instruction page:
[ http://www.taylortechnologies.com/Ch...P?ContentID=70 ]

Testing
To avoid damage to pools and spas from unbalanced water, test calcium hardness at least monthly. Calcium hardness is best monitored with a drop-count titration, as test strips can only measure total hardness. In addition, whereas test strips for total hardness have just four or five color blocks to cover a tremendously wide range—from 0 to 1,000 parts per million (ppm) with color blocks for 0, 100, 250, 500, 1,000, for instance—a drop test will allow you to approach the true concentration of calcium hardness in 10-ppm increments. This means if you're faced with wanting to balance water in a spa by increasing the calcium hardness from 60 ppm to 150 ppm, the strip can't help but the drop test can.

To perform a drop test, simply fill a test cell with sample water, add buffer and indicator reagents, and swirl to mix. The sample will turn red if calcium hardness is present. Next, add the calcium hardness reagent, swirling and counting each drop, until the color changes from red to blue. Finally, multiply the number of drops used by the equivalence factor in the test instructions to determine the calcium hardness level. The reading is expressed as parts per million of calcium carbonate.

The color progression in a hardness test is from red, to a mixture of red and blue, to blue. To be certain the color change is permanent, indicating you have reached the true endpoint, add one more drop of titrant. If the blue color remains unchanged, do not count this drop.

Beware the Fading Endpoint
Occasionally when testing calcium hardness you may get a purple endpoint instead of blue. This is called a "fading endpoint" and is due to interference from metal ions (most likely copper from algaecides, pipes, or source water). Retest, but prevent the interference by adding five or six drops of hardness reagent to the sample before adding the buffer and indicator. Then proceed as usual. Remember to count the drops of titrant added at the beginning when you calculate the total number of drops required to reach the endpoint.

Here's Taylor's image, from that page:


But, as you may realize, that picture shows a 'textbook' progression, which unfortunately, many pool water samples do not exhibit.

There is a useful post at Trouble Free Pools, here:
http://www.troublefreepool.com/consi...st-t20339.html

But, I think the most helpful element in that post is this one:

I just got off the phone with Jodi from Taylor. She was very helpful. She told me that the end-point is most definitely blue, and to ignore the steady purple color. In the case of the CH test, the sample may change to a purple color and remain that way for several drops, (exactly what I was seeing,) but that it will eventually turn blue, and that is when you start watching for the color change to stop. Part of the reason for this is that the R-0010 is sodium hydroxide, which raises the pH of the sample, thus making the reaction times longer. (This must also be the reason waterbear suggested the sample needed to be swirled a long time between drops?)

So, in my case, where I got a consistent purple at 18 drops and a consistent red at 29 drops, my CH is really 290.

She also told me that the same thing applies to the TA test, to an extent. The color might hang on grey for several drops, but should certainly turn to pink or red at some point. In that test, once you reach the pink stage, you might not ever get a true red, and the end point is where the change stops. (This change-cessation point on the TA test has been discussed in several other threads.)

So, I wasn't initially doing it wrong, after all. I wasn't wrong until I started actually thinking about it. (Imagine that!!!!!)

I know Jody (O'Grady => http://goo.gl/WE0cp ), and have found her generally knowledgeable and trustworthy. If you want to call Taylor, try to speak with her (or Wayne Ivusich, if you can reach him.)

[waterbear]

Many people do not run the calcium hardness test to endpoint but stop at the color change, it is important to keep titranting until endpoint is reached. I have seen samples where the calcium hardness was over 600 ppm, which is over 60 drops of titrant with a 25 ml sample and many people thing that it cannot require that many drops! However, it can! In some parts of the country CH well over that reading is not uncommon, nor is it uncommon to have very high calcium with new plaster! My first suggestion is to do the 10 ml test instead of the 25 ml test (10 drops buffer, 3 drops of indicator, and each drop of titrant equals 25 ppm calcium hardness).
Second, SWIRL AFTER EACH DROP FOR 20 TO 30 SECONDS OR USE A MAGNETIC STIRRER! The reaction IS slow and can appear to 'stick' at the violet in between color for several drops, particularly with the higher resolution 25 ml sample test!
Third, the first reagent is sodium hydroxide which causing the magnesium in the sample to precipitate out so yo are only testing for calcium hardness and not total hardness and is a reason to really swirl well for about 30 seconds after adding the first reagent to make sure the reaction carries to completion! Once again, a magnetic stirrer is useful here!