Big drop in TA, big spike in CH...I'm confused

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steveinaz

steveinaz

0
Mar 29, 2007
72
Southern Az
Pool Size
12900
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Numbers today, 53degree water. Pool is 1 year old. In ground, plaster/gunnite--apprx 13k gallon. Taylor test kit:
FC=7
pH=7.4
TA=50ppm (last year it was 130ppm)
CYA=70ppm
CH=825ppm!!! (last year was 325ppm)
SA=3800ppm

My kit shows 3/2019 exp dates on drops....but is always stored in a temp controlled environment. Any ideas what would cause CH to spike? I do use Natural Chemistry "Scale Free" at 6 ounces per month (works GREAT BTW).

The water looks great, crystal clear. I tested the CH twice to make sure--again, this fill is only 1 year old.
 
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CH test is sensitive to drop size. Wipe the tip in between drops and hold the bottle vertically and let the drop full form and fall off the tip. Forcing small drops will inflate your results.

As @aussieta suggested test your fill water. You have an autofill system?
 
Fill water measures at 300ppm. I do have auto fill. Keep in mind, I had a pool for 5 years in this same neighborhood (same water Co), but never experienced a spike like this in 1 year. I think I'm gonna have my pool builder test, and see what they get. I'm suspecting my reagents...but 1 year old seems a little young for the reagents to go bad on me.....
 
When was the last time you tested?

Based on the numbers, I might suspect that someone added a lot of acid, which could have dissolved calcium from the plaster.

Has the pool been circulating?
 
I suspect your CH is 825. I would not call a 500 ppm increase a "spike" in a years time in Arizona. I would say it's a lot but not unrealistic.

If you have stored your reagents as you report, they will not be the culprit.......High CH fill water and evaporation in Arizona is almost surely your issue

(Wiping the dropper tip for drop size control is not relevant for CH. That is for the TA test only.....no other tests are affected.)
 
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The scale stuff you add - it just keeps the scale from forming but the CH still builds in your water. I have the same water you do and I build from 300 to 800+ CH in 16 months. I just manage my CSI and get no scale.
 
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I think you nailed it with the evaporation theory. This Winter I left the pool uncovered just to make maintenance more convenient, and I think this is what caused the concentration of calcium. Looks like a drain and re-fill are in my future. Lesson learned.

Thanks all for the input.
 
duraleigh said:
I suspect your CH is 825. I would not call a 500 ppm increase a "spike" in a years time in Arizona. I would say it's a lot but not unrealistic.

If you have stored your reagents as you report, they will not be the culprit.......High CH fill water and evaporation in Arizona is almost surely your issue

(Wiping the dropper tip for drop size control is not relevant for CH. That is for the TA test only.....no other tests are affected.)
Click to expand...

I think you nailed it. Evaporation.
 

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Don't know exactly---don't have my notes in front of me, but TA is typically around 120, and high pH is constant fight (normally) in Southern Az, especially with a SWCG. There is a variable when comparing to my last pool of 6 years; the new pool has a variable speed/flow pump, it runs 23hrs a day (8hrs @ 2350rpm, the rest of the time @ 1200rpm) so I'm thinking the constant circulation is what may have dropped my TA. Normally it's a constant battle to keep TA down to 120. Then add to this, for the first time ever, I left the pool uncovered all Winter, so this would also possibly explain the lower TA as more CO2 was allowed to gas off. I run my pool all year, I just remove the Salt cell and put a bypass in when temps drop, then chlorinate with bleach in the Winter.

I'm gonna re-check fill water CH levels and just plan on doing an aggressive drain, re-fill. This time I'll keep the pool covered. I'm pretty sure evaporation is the culprit.
 
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TA can't drop on its own. Only acid can drop TA. If your fill water is 120, your TA is going to be at least 120 or higher.

Are you sure that the pH and TA of the fill water are still high?

Evaporation might be part of the calcium rise, but it's winter and evaporation should be low.

When is the last time that you checked the chemistry?

Your numbers make me wonder if someone added acid at some point.

Is that a possibility?

If yes, I would suspect that the pH and TA were very low and only rose as plaster dissolved and raised the pH, TA and calcium.
 
I'll have to re-check fill water TA/pH. Typically my pool requires about 12oz of muriatic every 4th day during the summer with the SWCG running. I check FC and pH weekly, other numbers are done in the Spring and Fall. I'm the only one that does maintenance on the pool.
 
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I'm able to maintain 7.4-7.6 with 12oz of muriatic a week. (every Saturday) Requires more acid when the SWCG is running. Cell came out around mid November when the water got cold. Usually by mid May, I can reinstall it. My pool is not heated.

Pic taken 3 March:
 

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I'm sure that evaporation can account for some of the increase, but 500 ppm in 4 to 6 months of cold weather seems very aggressive.

Mknauss notes a similar increase in 16 months.

You're keeping the pH and the CSI too low and it's probably dissolving the plaster some, which would account for some of the calcium increase.
 
We ARE crazy dry...even more so in the Winter. Our temps are about 6-8 degrees cooler than Tucson, due to our 4600ft elevation. We're about 85 miles South of Tucson. Right near the border.
 
If you are using a scale inhibitor, there is a high degree of likelihood that it will interfere with the CH test as the CH test is a chelation test (EDTA is the titrant). So your water now has competing chelating agents in it that can mask the test results. So, it is entirely possible that your pre-winter CH test results were artificially lower than the real value because of the scale inhibitor.
 

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