My calcium spikes

[Green Goblin]

Maybe someone has an idea about this:

I have maintained the same pool for 5 years. For the first 3, the Calcium Hardness (CH), never exceeded 400.

In March 2015, I purchased new testing kit materials (fresh reagents for the new season). All of a sudden my CH level was 550 with the new kit, and 350 with the old kit. I talked with some folks about this and did some research on it. Pool looked and acted fine. Pool store check was 425. No detectable copper in the pool. Eventually I attributed the CH increase to when we restained the concrete deck, some muriatic acid was used in the prep, then it was power washed. I figured some dissolved calcium got in that way.

We had a rainy period, and there was a lot of rainfall and pumpout, and slowly the CH drifted down. I did not any significant fill water from any source other than rainfall for the rest of the year. In December it was 440. I thought I was close to home on solving the problem.

Until... I bought new testing kit materials again (fresh reagents every year, right?). CH now 580. Copper 0. We did powerwash the deck, but we didn't use any acid or restain it. Certainly some hose water went in with the powerwash, but not even an inch, and the hose water is CH 80. In my 5 years, I have never added calcium or copper containing products to the pool.

Running a few numbers, to go from 440 to 580 in my 13500 gallon pool would take 17+ pounds of calcium product-- so where the heck could this have come from? The only thing I can figure is the pool walls-- where else is 17 pounds of calcium hanging out?

The confession: Due to previous stability and arrogance, I generally only check the CH every 2-3 months. I have learned my lesson here, and will check it more often.

The other theory: perhaps older reagents are more likely to test lower CH levels, and the newer reagents are more accurate, and really my CH is high all along?

Random bits of information:
I use a speedstir for every test.
Pool looks great to me
Pool is in Gainesville,FL
Pool is solar heated, and often kept very warm 86-92ish when we can
Pool is covered from about October to May
It's a salt pool
pH pretty tightly kept 7.4-7.8ish
We suspect copper was previously used in the pool, prior to 5 years ago due to the coloration of the rim around the light, and there are what appear to be some copper stains on the surface too-- stable for years though.




Thanks for any and all ideas.

 

[Patrick_B]

Test kit accuracy differences, testing error or variation, evaporation, and source water changes could all be contributors. Those items would be the first I would seriously consider. Where you are is very manageable, so I'd not worry too much about the past readings, but monitor more frequently as you're planning and see where it goes.

 

[JoyfulNoise]

It is possible for the CH reagents to age. The indicator dye (R-0011L) is the least stable of all the chemicals and has been known to go bad. The titrant (EDTA) can go bad over time too without any indication. You also mention copper as a possible source of contamination and that does affect the test too. Unfortunately copper is not easy to test for as you have to have a kit that can test for both dissolved copper as well as total copper. Unless you have a constant source of copper (like a bad heat exchanger or old copper pipes), the copper concentration should lower over time and not be a problem.

I would suggest you run your CH test more consistently over the next swim season (maybe twice per month?). Make sure you are in bright outdoor lighting and try this modified test procedure -

Add the required amount of calcium buffer solution (R-0010)
Add half the number of expected drops of the calcium titrant (R-0012)
Add the calcium indicator dye (R-0011L)
Add the remaining calcium titrant (R-0012) until blue endpoint is reached

Be sure to add up both R-0012 drop counts as your final number. Let us know if your results get more consistent.

 

[Patrick_B]

What does Taylor say the copper interference level is Matt if you know off hand?

 

[JoyfulNoise]

What does Taylor say the copper interference level is Matt if you know off hand?

You know something, the Taylor website says that the R-0012 is formulated with inhibitors to prevent metal interference (that's new to me, I'd never seen that detail listed before). So, if the OP's reagents are new, then I think copper can be crossed off the list as a suspect. In the past, metals were an issue which is why they had a special procedure for fading end points (adding some R-0012 after the R-0010 to chelate metals). So they must have changed their formulation of the R-0012.

I suspect a high enough metal load would still cause a problem for the test but you'd likely be at the point of seeing metal stains in the pool.

 

[OTPirate]

You can also purchase R-7063 (Calcium Hardness Standard 200 ppm) at Taylor or tftestkits.net to test your testing methods and/or your reagents. It is like having the answer sheet to a test. Remember to use the standard solution like it is pool water. It may help to rule out expired reagents.

 

[JoyfulNoise]

You can also purchase R-7063 (Calcium Hardness Standard 200 ppm) at Taylor or tftestkits.net to test your testing methods and/or your reagents. It is like having the answer sheet to a test. Remember to use the standard solution like it is pool water. It may help to rule out expired reagents.

Excellent point!

If someone's R-0012 reagent were bad, there would be no way to know because, unlike the R-0011L indicator, there's no visual indication that it has gone bad.

 

[otter86753]

You can also call Taylor Technologies with the lot number and they will tell the efficacy if the reagent was stored properly.

 

[Patrick_B]

You know something, the Taylor website says that the R-0012 is formulated with inhibitors to prevent metal interference (that's new to me, I'd never seen that detail listed before). So, if the OP's reagents are new, then I think copper can be crossed off the list as a suspect. In the past, metals were an issue which is why they had a special procedure for fading end points (adding some R-0012 after the R-0010 to chelate metals). So they must have changed their formulation of the R-0012.

I suspect a high enough metal load would still cause a problem for the test but you'd likely be at the point of seeing metal stains in the pool.

Interesting point, and I had no idea they made such a change.

 

[Green Goblin]

Thanks for all of these helpful ideas-- particularly the idea of using the standard solution as a control so that I know the test is accurate.

Today I'm in the middle of partial drain/refill procedure, which is painful for many reasons but at least this will drop the level somewhat. I'm not able to drain off enough water to do a single drain and refill (well, not able to do this in a practical and easy way), so it becomes a serial dilution which is costly in terms of time/water/chemicals.

We had a ton of yellow pollen in the pool this year-- when I cleaned my filter out the water in there looked like yellow paint (yes I drained this out and cleaned it). I noticed the calcium spike after this and I know there is some calcium in pollen, but I don't know how much. I figure if it were a pollen thing everyone would know about it, since there must be millions of pools covered in yellow pollen during the spring.

 

[Green Goblin]

"I suspect a high enough metal load would still cause a problem for the test but you'd likely be at the point of seeing metal stains in the pool."

There appear to be copper stains on the surface that have been there for more than 5 years, but copper in the water appears to be undetectable, and the pool has been drained and filled twice over those 5 years (mostly drained at least). Also the CH testing previously tested out lower both on my home tests and at the pool store.