PH Rising

loganparker

New member
Apr 25, 2018
3
Salado/Texas
I've had my pool for 4 years and this is the first time I've had trouble managing my PH. I only use liquid chlorine, muriatic acid and baking soda. So this the scenario I encounter weekly. My FCL is 1.6, PH is 8.0 and TA 80. I add 2 gallons of chlorine and 1 gallon of muriatic acid. Next day the levels are FCL 4.8, PH 7.5 and TA 63. 3 days later the FCL is back to 1.6, PH is 8.0 and TA is 63. I typically have to add 15 lbs of baking soda weekly to keep the TA around 80-90 while this is going on. Before this year my PH always stayed in the 7.5-7.6 range with only minimal muriatic acid. My CYA is currently 47. Thanks for any advice.
 
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loganparker

New member
Apr 25, 2018
3
Salado/Texas
Welcome to the forum!
How are you testing your pool water chemistry?
I suggest you read ABC's of Pool Water Chemistry.
I use a LaMotte ColorQ. I’ve used it for 4 years. I think the advice to read the ABCs is solid and it never hurts to refresh. I assume you suggested this based on my CYA and FCL levels. That being said, I’ve never had a problem keeping my PH at 7.6 until recently. I’ve never run my FCL much higher than 4-5 and never had a PH issue until recently. I suppose what I’m asking is if anyone has an idea what may be causing it to rise so quickly considering I haven’t done anything different the past 4 years and only now it’s become an issue. Thanks
 

mgtfp

Bronze Supporter
Mar 5, 2020
433
Melbourne, Australia
You are adding way too much MA. 1 gal of full strength MA will get your pH below 7, and gets your TA down - that is unexpected. And the rate of pH-rise is a lot faster at lower pH, it doesn't buy you much time to bring pH that low. You should add less more often.

Same for chlorine. Completely normal that your FC drops back to 1.6 in 3 days. Add chlorine daily to keep it more constant. That also affects your pH swing. We say that bleach has no net effect on pH, i.e. the whole chlorination cycle is pH-neutral - adding bleach raises pH, the following chlorine usage brings it back down. As long as your FC stays fairly constant, you won't notice much of that.

What happens in your case is the following (leaving the MA out of the game for now):
- starting with pH 8.0, TA 80 and FC 1.6.
- Adding 2 gal of 6% bleach brings you to FC 6.3, pH 8.4 (I assume you used lower strength bleach, otherwise your FC should have got a lot higher)
- 4.7ppm of chlorine usage over three days brings FC back down to 1.6 and pH back to 8.0
- Above pH 8, CO2 outgassing will be very small, probably hardly any pH-drift in that time, i.e. in the end you will end up close to pH 8 again, without having used any MA. But within the cycle, pH will be too high.

Due to the large FC swing you are allowing, you also have a considerable pH cycle. It is important to always measure and compare your pH at the same point in the cycle. If you measure one day before adding bleach and the next time after adding bleach you will likely overreact with your MA. Remember, the chlorination cycle is pH-neutral. But the larger the FC-swing you allow is, the larger the pH-swing will be in your cycle. But the pH-rise after adding bleach will come down on it's own, no need to (over-) correct that with MA. Your MA additions have to be based on pH-measurements that are at the same point in your chlorination cycle.

If you add less chlorine more often, you won't hardly notice the swing. In your case, you went from FC 6.3 to 1.6 in 3 days, about 1.6 FC loss per day, not bad actually. If you added 1.6ppm worth of chlorine each day, above scenario would change to this:
- starting with pH 8.0, TA 80 and FC 1.6.
- Adding 86 oz of 6% bleach brings you to FC 6.6, pH 8.1
- 1.6 ppm of chlorine usage brings FC back down to 1.6 and pH back to 8.0

Much smaller pH swing within your chlorination cycle, you won't be tempted to over-correct with MA.

And just for completeness, your example including the MA addition:
- starting with pH 8.0, TA 80 and FC 1.6.
- Adding 2 gal of 6% bleach brings you to FC 6.3, pH 8.4
- Adding 1 gal of full strength MA brings pH to about 7.0 and TA to 64.
- The chlorine usage wants to reduce your pH further, but CO2-outgassing is so fast at this low pH, that the pH-rise by outgassing will likely overcompensate (you were already back at 7.5 after just one day).
- In the end, you will be very quickly to where you started with your pH, but you have wasted a gallon of MA on the way.

You want to have that middle scenario, just a bit lower in pH. Target your pH around 7.6 to 7.7, add chlorine on a daily basis to keep your FC more constant, and you'll be fine. Make the pH-measurements always at the same point in the cycle for your MA additions. And keep TA in the TFP recommended range. Also important to know your CH. If your CH is really high, then pH 7.6 to 7.7 might not work for you, you'd have to watch your CSI in that case.

Regarding the articles that Marty suggested: Not just FC/CYA. Also recommended levels, TA, CH, CSI - the whole lot, actually. And testing: We recommend titration tests based on Taylor reagents. That ensures that we are all using the same tests, allowing us to trust your test results and to put them into the right context.

And use PoolMath to calculate how much chemicals to add.
 

loganparker

New member
Apr 25, 2018
3
Salado/Texas
You are adding way too much MA. 1 gal of full strength MA will get your pH below 7, and gets your TA down - that is unexpected. And the rate of pH-rise is a lot faster at lower pH, it doesn't buy you much time to bring pH that low. You should add less more often.

Same for chlorine. Completely normal that your FC drops back to 1.6 in 3 days. Add chlorine daily to keep it more constant. That also affects your pH swing. We say that bleach has no net effect on pH, i.e. the whole chlorination cycle is pH-neutral - adding bleach raises pH, the following chlorine usage brings it back down. As long as your FC stays fairly constant, you won't notice much of that.

What happens in your case is the following (leaving the MA out of the game for now):
- starting with pH 8.0, TA 80 and FC 1.6.
- Adding 2 gal of 6% bleach brings you to FC 6.3, pH 8.4 (I assume you used lower strength bleach, otherwise your FC should have got a lot higher)
- 4.7ppm of chlorine usage over three days brings FC back down to 1.6 and pH back to 8.0
- Above pH 8, CO2 outgassing will be very small, probably hardly any pH-drift in that time, i.e. in the end you will end up close to pH 8 again, without having used any MA. But within the cycle, pH will be too high.

Due to the large FC swing you are allowing, you also have a considerable pH cycle. It is important to always measure and compare your pH at the same point in the cycle. If you measure one day before adding bleach and the next time after adding bleach you will likely overreact with your MA. Remember, the chlorination cycle is pH-neutral. But the larger the FC-swing you allow is, the larger the pH-swing will be in your cycle. But the pH-rise after adding bleach will come down on it's own, no need to (over-) correct that with MA. Your MA additions have to be based on pH-measurements that are at the same point in your chlorination cycle.

If you add less chlorine more often, you won't hardly notice the swing. In your case, you went from FC 6.3 to 1.6 in 3 days, about 1.6 FC loss per day, not bad actually. If you added 1.6ppm worth of chlorine each day, above scenario would change to this:
- starting with pH 8.0, TA 80 and FC 1.6.
- Adding 86 oz of 6% bleach brings you to FC 6.6, pH 8.1
- 1.6 ppm of chlorine usage brings FC back down to 1.6 and pH back to 8.0

Much smaller pH swing within your chlorination cycle, you won't be tempted to over-correct with MA.

And just for completeness, your example including the MA addition:
- starting with pH 8.0, TA 80 and FC 1.6.
- Adding 2 gal of 6% bleach brings you to FC 6.3, pH 8.4
- Adding 1 gal of full strength MA brings pH to about 7.0 and TA to 64.
- The chlorine usage wants to reduce your pH further, but CO2-outgassing is so fast at this low pH, that the pH-rise by outgassing will likely overcompensate (you were already back at 7.5 after just one day).
- In the end, you will be very quickly to where you started with your pH, but you have wasted a gallon of MA on the way.

You want to have that middle scenario, just a bit lower in pH. Target your pH around 7.6 to 7.7, add chlorine on a daily basis to keep your FC more constant, and you'll be fine. Make the pH-measurements always at the same point in the cycle for your MA additions. And keep TA in the TFP recommended range. Also important to know your CH. If your CH is really high, then pH 7.6 to 7.7 might not work for you, you'd have to watch your CSI in that case.

Regarding the articles that Marty suggested: Not just FC/CYA. Also recommended levels, TA, CH, CSI - the whole lot, actually. And testing: We recommend titration tests based on Taylor reagents. That ensures that we are all using the same tests, allowing us to trust your test results and to put them into the right context.

And use PoolMath to calculate how much chemicals to add.
Thank you for the thorough analysis and explanation. Just to provide a bit more information, I always test my FC, pH and TA at the same time and add chemicals accordingly. I also use a chlorinating liquid with 10% sodium hypochlorite. That being said, I will take your advice and add less chemicals more frequently. Hopefully that will normalize my numbers. Thanks again.