Need advice to correct chlorine lock

[jrh]

I had my pool water tested today at a dealer using the BioGuard ALEX system. Here is how it tested:

pH: 7.2
Total Chlorine: 5.5
Free Chlorine: 2.8
CYA: 127
Total Alkalinity: 97
Adjusted Total Alkalinity: 59
Total Hardness: 276
TDS: 500
Saturation Index: -0.5

I was told to add the following:

> Total Alkalinity: Add 25.5 lbs of Balance Pak 100 (sodium hydrogen carbonate)

> pH: Add 3.25 lbs of Lo 'N Slo (pH decreaser)

> Chlorine: Add 14 bags of Burn Out 3 (Calcium Hypochlorite - 57.8%) to eliminate the chlorine lock

My in-ground pool is about 23,000 gallons (17' x 32' rectangle, 3' shallow end, 8' deep end, angled corners). I use Doheny 3" chlorinating tabs (99% trichloro-s-triazinetrione), 3-8 oz tabs every 4 days. I also use Doheny Super Shock (Calcium Hypochlorite: 68%) occasionally. I used 2 lbs when I opened the pool 5/26 and 2 more lbs. on 7/1. I run the pool filter about 12 hrs. per day.

The water was a little cloudy when I opened the pool in the spring (5/26). It took a couple days to clear up and since then has remained clear. The 3" tabs, added to the skimmer basket, completely dissolve in 4 days which is why I add them every 4 days. The free chlorine level stays about 3 to 5. I've sometimes waiting a day or two and run the filter without the tabs because the chlorine level has been good, at least I think it is.

I've chatted with a person at Doheny's and found out that the 3" tabs do have stabilizer in them. He said that shocking the pool would not fix the chlorine lock problem. His recommendation was to drain 1/3 to 1/2 of the pool water and refill with fresh water. Then switch to a product with a lower amount of stabilizer.

I know that I can adjust the TA using baking soda and I will probably have to adjust the pH after that, but I'm not sure what to do about the chlorine issue. Can anyone suggest a way to attack the chlorine problem?

 

[JasonLion]

Welcome to TFP!

There is no such thing as "chlorine lock". That is just a phrase pool store people use to describe things they either don't understand or don't feel like explaining to you.

I'm not sure if I trust those test results. Pool stores are not known for accurate water testing. Assuming everything is correct:

Replacing water is indeed your best option to lower CYA. You have been using trichlor tablets, which are constantly adding CYA, which eventually gets too high and causes problems, like the ones you are experiencing now.

There is no conceivable reason to add Lo 'N Slo. That is a completely ridiculous recommendation. Also, 25 lbs of TA Increaser is way too much.

 

[woodyp]

Two partial drains of 1/3 each is the best thing you could do to manage that cya level. PH is bottom end now. What does that tell you about their recommendations? Most here use plain old bleach to sanitize without a SWG. Welcome!

 

[jblizzle]

I agree with Jason.

I can only think that they are saying to add the Lo n slo to counter any pH rise that results from all that TA increaser.

Don't you just want to trust a company that is more than happy to sell you products that cancel each other out? Still not as bad as the one case where someone was told to add pH UP and ph DOWN ...

 

[jrh]

Thanks for the welcomes and for the replies!

I guess what I need to do is get a good test kit. If we assume for now that the pool store test is accurate, I should drain 1/3 to 1/2 of the pool water, add baking soda to adjust TA, and add something to reduce the pH if needed because of the baking soda? I can get Pool-Trol pH Minus (Sodium Bisulfate) pretty cheap ($7.99/5 lbs.) if that's any good.

Once I have the CYA reduced and the TA and pH adjusted, will I still have the problem with combined chlorine?

Reading through the forum a bit, I see that most people use bleach or liquid chlorine. I can get 12.5% liquid chlorine from the pool store. How much would I need use and what is the best way to apply it?

Jason, what amount of baking soda would you recommend to increase the TA? What level should it be at?

 

[jblizzle]

The ph and TA numbers are fine, no need to adjust them, especially if you are going to replace water.
If you are not salt water, then you need to replace around 70% of the water to get to our recommended CYA levels.

To get rid of the CC you need to add a lot of liquid chlorine.

I suggest you read some more of Pool School to get a better feel for the chemistry and the levels we recommend. Yes, liquid chlorine is what you want to use after lowering the CYA. And these are the Recommended Test Kits.

Some reading:
ABCs of Water Chemistry
Recommended Pool Chemicals
How to Chlorinate Your Pool
pool-school/recommended_levels

 

[linen]

Welcome to tfp, jrh

I guess what I need to do is get a good test kit.

Many of use have the tf-100 since it is the best value. See: http://www.troublefreepool.com/pool-school/pool_test_kit_comparison

If we assume for now that the pool store test is accurate

I wouldn't. cya is one pool stores get wrong more than right. I would test it yourself before doing any drain/refills.

I can get Pool-Trol pH Minus (Sodium Bisulfate) pretty cheap ($7.99/5 lbs.) if that's any good.

It works, but we recommend using Muriatic acid which should be significantly cheaper than that dry acid.

I really would not trust those test results. Get the appropriate kit and in the meanwhile scour through pool school (link always near the upper right).

Once I have the CYA reduced and the TA and pH adjusted, will I still have the problem with combined chlorine?

CC is one sign of something (algae) growing in your pool. The SLAM process will take care of it. See: http://www.troublefreepool.com/pool-school/shocking_your_pool

 

[ComputerGuyInNOLA]

Does your pool have a chlorine odor? With such a high CC level I assume it would.

 

[techguy]

If this were me:
1. order the test kit. I am going to guess it cost less than the CalHypo the LPS was going to sell you.
2. start the drain to fix your CYA
3. Read Pool School and understand the CYA effects on chlorine
3a, Get 10 gallons of bleach/liquid chlorinator from your favorite box store, a bottle of 32 baume MA from HD or Lowes
4. start the refill with enough liquid chlorine based on your estimated CYA after the change
5. start testing with the TF-100 and make educated decisions with confidence
6. lose the business card to that pool store.

 

[jrh]

Last summer, I continued my normal chemical usage and didn't have any noticeable problems the whole summer. I opened the pool a couple weeks ago and the water was clear. I bought a TF-100 test kit and tested the water. These are the readings I got:

pH: ~ 7.0
Free Chlorine: 2.5
Combined Chlorine: <0.5
CYA: ~55
Total Alkalinity: 200
Calcium Hardness: 325

When doing the combined chlorine test, the water was just barely pink. Adding one drop of the R-0871 cleared it up, so I think it was probably less than 0.5. Since I didn't do anything to correct a combined chlorine problem, I'm guess that the pool place test wasn't very accurate. Would the test results that I got with the TF-100 test indicate that there isn't a combined chlorine issue?

The only problems that I see are low pH and high TA. Any recommendations on how I should adjust my water?

 

[jblizzle]

I am a little confused about your statement about the "pool place test" being accurate. Are you talking about the results from last July?

Make sure you keep the pH in the 7s and you need to raise your FC level ... for a CYA of 55ppm, you should never let the FC get below 4-5ppm according to the FC/CYA Chart.

If you only need one drop to clear the CC test, that is a good thing.

 

[jrh]

Right, I don't think the pool place test from last year was accurate. I don't think there was a combined chlorine problem as their test indicated.

The 2.5 ppm chlorine reading was the level when opening the pool. I have since increased the level and have been trying to keep it at about 3ppm. I will try to keep it a little higher at 4 or 5.

My understanding is that I should use 20 Mule Team Borax to increase the pH. How much should I add and what level should I be at? About 7.5?

 

[jblizzle]

No, you need to keep FC ABOVE 4-5ppm. So you should likely target around 7ppm everyday so it will not drop to under 4.5ppm or so by the next day.

The pH should just be anywhere in the 7s. Use PoolMath to calculate how much you need to add for a given adjustment.

 

[svenpup]

If you are new to PoolMath, make sure that you enter all of the "Now" values going down the left column. pH changes are affected by TA. All changes are affected by Size.