Chlorine/PH relationship

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mavrick6382

mavrick6382

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Apr 14, 2017
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Cave Creek, AZ
Hello, a couple of months ago I had an algae bloom infiltrate my pool. I made the mistake of failing to clean my filter AND shock the pool properly. I just kept adding tabs and the algae problem persisted. I finally wised up and cleaned out my filter cartridges, but the weeks I spent adding pucks caused my CYA to spike to 180. I drained the pool (almost entirely), added stabilizer to return my CYA to its optimal target level of about 50, and SLAM'd using liquid chlorine. As of today the pool is crystal clear and back in balance.

I have stopped using tabs and solely use liquid chlorine from Home Depot. My question is around the relationship between FC and pH. My CYA is about 50 or so, and according to the Chlorine/CYA Chart my Target FC is 5.7. As of Monday the 29th my FC was a little low (at 4) but my pH was perfect (at 7.5/7.6). I added chlorine that morning and as of today the chlorine is 5.5 but my pH is back up to 7.8. I feel like I am constantly going back and forth between slightly lower than target FC but perfect pH, and target FC but high pH.

Any thoughts or suggestions? I use a Taylor K-2006 test kit, fyi.
 
Looking at the [FC/CYA][/FC/CYA], with a CYA of 50 your FC minimum is 4 any your target is a range of 6 to 8.

You previously used tabs and they are very acidic, so they masked the normal rise of pH in your pool.

Liquid chlorine is basically pH neutral, so now you see the normal pH rise and now need to keep it in check with the addition of acid.
 
mavrick6382 said:
I have historically used Pool Time pH down granulars from Home Depot. Should I be using a liquid muriatic acid instead? Does it matter?
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Yes and yes.

You can do a search for "Pool Time Ph Down" in the TFP search box for more info. Here's one thread about it:

Muriatic Acid vs. PH Down -- compelling reasons for MA?

mavrick6382 said:
@jamesw, I am not sure I have ever tested CSI. Does the Taylor K-2006 have a test for that?
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No test for it. You plug your test results into PoolMath, filling in all the fields (important!), and you'll see your CSI value near the bottom. CSI is a mathematical result calculated from the other values for which you test.

This from the little box in Pool Math's CSI section:

Calcite Saturation Index - requires pH, TA, CH, CYA, Temp, uses Borate, Salt.
Less than -0.6 is suggestive of problems for plaster, tile, stone, and pebble pools.
Greater than 0.6 is suggestive of problems for all pools.
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I think of CSI as a sort of overall summary of my pool's chemistry. My personal goal includes stretching my new pebble finish for the maximum number of years possible. I'm shooting for 30. I try to keep each individual chemical level near the middle of the range that's appropriate for my pool, and monitor CSI as a guide for determining the health of my water, in terms of my longevity goal. If my CSI is out of the range that's appropriate for my pool and its equipment, while all the other chemicals are in range, then I adjust pH until my CSI is happy. That's my MO... It's all pretty simple, really.

To date, I've been able to maintain near-perfect levels, including CSI. I poured in the required sequestrant when my finish was brand new, and since then I've used only four chemicals in my pool: chlorine, muriatic acid, cyanuric acid and salt. That's it. I don't even pour the testing chemicals back into the water. One happy camper here. Not a spec of scale or algae anywhere so far, and the water looks and feels fantastic.
 
I'll move to liquid acid and will run the numbers in PoolMath to get the CSI.
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Mavrick, welcome to the forum! :wave: As you can see, pool advise is something we have plenty of here at TFP. Being an AZ resident, unless Cave Creek has an unusual soft water source, you probably know the story about hard water in your area. For that reason we tend to push your pool knowledge into areas not normally monitored by others around the country - like CSI. I just wanted to pass along that for the most part, if you keep all your TFP water parameters within the recommended ranges, the pool's CSI will take care of itself. Just try not to let it become obsessive …… yet. :wink: Once you get hooked on TFP water, there's no turning back. You've see/heard the explanations above, so as your TFP knowledge grows (or your CH level next season) , CSI may become a more important issue for you. Enjoy the forum and let us know if you have more questions.
 

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Texas Splash, thanks so much! I have come across this forum on and off for the past 5 years and for some reason I didn't really dive in until this year. I kept falling into the Leslie's trap and they fail every time. When my pool had an algae bloom recently (what set all this off), their test showed a 180 CYA and they said nothing about it. Just tried to sell me more stuff to throw in the pool...including phosphates! TFP is how I found out that the CYA needed to come down first, and the only way to do that was by draining. I fully subscribe to the idea of taking care of my own pool and using as few chemicals as possible. You guys have been super helpful and I can't thank you enough. I look forward to learning more.
 
Trying to determine my CSI. So here are the stats I was able to collect:

pH = 7.8
TA = 90
CH = 475 (that's with a full pool drain in the last 2 months)
CYA = 50
Temp = 69
Borate = ?
Salt = ?

Do I need to buy separate test kits for Borate and Salt? I don't see that my Taylor K2006 has those tests.
 
mavrick6382 said:
Trying to determine my CSI. So here are the stats I was able to collect:

pH = 7.8
TA = 90
CH = 475 (that's with a full pool drain in the last 2 months)
CYA = 50
Temp = 69
Borate = ?
Salt = ?

Do I need to buy separate test kits for Borate and Salt? I don't see that my Taylor K2006 has those tests.
Click to expand...
There are separate kits, but unless you have added borates or salt, assume 0 with your fresh fill.
 
I get a CSI of about 0.32 using your current numbers. That's ok, but a little high.

I would keep the pH at about 7.7 to 7.6 until the water gets cooler to stay below 0.30.

Recheck the CSI periodically to make sure that you're in range.

As you lower the pH to 7.6 or 7.7, the TA will drop to about 70 or 80.

A lower TA and cooler water will lower the CSI and then you can raise the target pH back to 7.8 or 7.9 to compensate if necessary.

Don't add anything to raise the pH, it will raise on its own.

Don't raise the TA. A TA of 60 to 80 tends to be good for most pools with a pH of about 7.8.

When the water begins to warm up again, you will probably need to keep the pH and TA a little bit lower to keep the CSI in check.
 
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