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High Ph, Low Ta -- Viscous Cycle!


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Have been taking care of this pool for a year, and while the water is always clear, I find myself in a cycle:

* pH high, TA low -> Add Muriatic acid

* pH good, TA low -> Add Alkalinity Up

* pH climbing, TA good

* pH high, TA good -> Add Muriatic acid

* pH good, TA low -> Add Alkalinity Up

* pH climbing, TA good

...

It seems that adding Muriatic acid reduces TA (I think I've read it turns it into H2O+CO2+NaCl, jacking up my TDS).

And it seems that either adding Alkalinity Up (Baking Soda) increases pH OR something else is causing my pH to climb.

Anyone have an idea what's going on? Does this go on all year for some folks?

Details that might be useful: outdoor in-ground plaster pool, water clear (no probs keeping it that way, save the above), CYA now ~40, CH=~200, pH range=7.4 .. 8.0, TA range=75..120, trichlor pucks, rarely need to shock, pool open for ~10 weeks now and have been in this cycle ever since, avg temps now ~90F day / 75F night, full-sun most of the day, circulates ~6 hrs/day.

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Don't try and raise the Total Alkalinity (TA) if the pH tends to be rising. Keep the TA lower. It is true that normally you would have a higher TA when using Trichlor because it is acidic, but if your pH is rising over time then you could have a lot of aeration of the water. The pH rises because carbon dioxide outgasses from the water as pools are intentionally over-carbonated. Try leaving the TA around 80 ppm and see what happens. If the pH tends to drop, then raise the TA a bit; if the pH is more stable, then you may find the TA slowly dropping over time (due to the Trichlor acidity) in which case you can add a small amount of baking soda to raise it back again.

Also, you are correct that acid lowers both TA and pH, but baking soda mostly raises TA though depending on how you add it, the pH can rise some as well. If you add the baking soda more slowly into a return flow so that it mixes well, you may get less of a pH rise. If you dump it in one place too quickly, then more carbon dioxide can outgas causing the pH to rise.

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Don't try and raise the Total Alkalinity (TA) if the pH tends to be rising. Keep the TA lower. It is true that normally you would have a higher TA when using Trichlor because it is acidic, but if your pH is rising over time then you could have a lot of aeration of the water. The pH rises because carbon dioxide outgasses from the water as pools are intentionally over-carbonated.

Hmm. That's really good food for thought. So how long I leave the pool circulating each day, how long the Polaris runs, and (maybe even moreso) how much flailing around my Polaris does when it's running could be killing my Alk/carbonation and raising my pH (?)

Now that I think of it this way, we did get a new Polaris this past winter -- the old one had the energy of an old grandma compared to this new one that frequently breaks the surface shooting water and splashing about with its tail. And we didn't have the Alk/pH problem last year with the old Polaris.

Try leaving the TA around 80 ppm and see what happens. If the pH tends to drop, then raise the TA a bit; if the pH is more stable, then you may find the TA slowly dropping over time (due to the Trichlor acidity) in which case you can add a small amount of baking soda to raise it back again.

Will do. Think I might also try running the Polaris less time each day (and make it a little less spritely) to see if I can make a dent in the rate-of-pH fall with that.

Also, you are correct that acid lowers both TA and pH, but baking soda mostly raises TA though depending on how you add it, the pH can rise some as well. If you add the baking soda more slowly into a return flow so that it mixes well, you may get less of a pH rise. If you dump it in one place too quickly, then more carbon dioxide can outgas causing the pH to rise.

Ok. So in general I don't need to worry about baking soda clogging up the filter and driving up the pressure until it goes into solution?

Thanks for the ideas!

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I would add the baking slowly over a return flow in the deep end. You can add it to the skimmer if you like and it dissolves fairly quickly, but you shouldn't be dumping large chunks of any chemical no matter where you add it.

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  • 1 month later...
Don't try and raise the Total Alkalinity (TA) if the pH tends to be rising. Keep the TA lower. ... Try leaving the TA around 80 ppm and see what happens.

Just a follow-up for those searching the forums, allowing the TA to run lower than the 100-120ppm recommended for Trichlor was the ticket. My pH and TA is much more stable with a TA ~65ppm, requiring very little acid to keep the pH between 7.4-7.6, and only a little baking soda once every 3 weeks or so if my TA dips a little lower.

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Have been taking care of this pool for a year, and while the water is always clear, I find myself in a cycle:

* pH high, TA low -> Add Muriatic acid

* pH good, TA low -> Add Alkalinity Up

* pH climbing, TA good

* pH high, TA good -> Add Muriatic acid

* pH good, TA low -> Add Alkalinity Up

* pH climbing, TA good

...

It seems that adding Muriatic acid reduces TA (I think I've read it turns it into H2O+CO2+NaCl, jacking up my TDS).

And it seems that either adding Alkalinity Up (Baking Soda) increases pH OR something else is causing my pH to climb.

Anyone have an idea what's going on? Does this go on all year for some folks?

Details that might be useful: outdoor in-ground plaster pool, water clear (no probs keeping it that way, save the above), CYA now ~40, CH=~200, pH range=7.4 .. 8.0, TA range=75..120, trichlor pucks, rarely need to shock, pool open for ~10 weeks now and have been in this cycle ever since, avg temps now ~90F day / 75F night, full-sun most of the day, circulates ~6 hrs/day.

I'm the pool operator at the YMCA in Albany, OR and our fill water is 8.2pH and alkalinity is 30, pretty much what you're describing here. Here's how you do it and it's very simple.

To raise the Alk....Pump off and water motionless, add bicarb to the deep-end. Allow to sit for 2-3 hours, turn pump on and allow to circulate for 1 complete turnover, then re-test. Make another small adjustment if needed.

Lower alk....same procedure, just substitute acid for bicarb.

Raise pH....water circulating and pump on, add bicarb around the perimeter of the pool

Lower pH....same procedure just use acid

Start first with the alkalinity, then do the pH. You shouldn't need to raise the pH too often because pH will naturally rise. Keep your pH around 7.6-7.8. not 7.2.

Most information on how to balance pools comes from your local water company. It's called the Langelier Index, which you've probably heard before. Great for public water systems, not so much for pools. And don't worry about your chlorine not being active enough. At 7.2-7.4pH, your chlorine is about 50% active. At 7.6-7.8, it's 45% active. You're going to be using too much acid to keep the pH at 7.2.

Alkalinity

pH

Maintenance Tips

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I'm the pool operator at the YMCA in Albany, OR and our fill water is 8.2pH and alkalinity is 30, pretty much what you're describing here. Here's how you do it and it's very simple.

To raise the Alk....Pump off and water motionless, add bicarb to the deep-end. Allow to sit for 2-3 hours, turn pump on and allow to circulate for 1 complete turnover, then re-test. Make another small adjustment if needed.

Lower alk....same procedure, just substitute acid for bicarb.

Raise pH....water circulating and pump on, add bicarb around the perimeter of the pool

Lower pH....same procedure just use acid

Start first with the alkalinity, then do the pH. You shouldn't need to raise the pH too often because pH will naturally rise. Keep your pH around 7.6-7.8. not 7.2.

Most information on how to balance pools comes from your local water company. It's called the Langelier Index, which you've probably heard before. Great for public water systems, not so much for pools. And don't worry about your chlorine not being active enough. At 7.2-7.4pH, your chlorine is about 50% active. At 7.6-7.8, it's 45% active. You're going to be using too much acid to keep the pH at 7.2.

Alkalinity

pH

Maintenance Tips

If you noticed, Dark Helmut solved his problem by lowering the TA level which reduced the rate of pH rise. You don't lower the TA different than the pH using the techniques you described (i.e. pump off vs. on). The reason why it doesn't matter how you add the acid is described here. Both pH and TA are lowered with acid addition. If you want to lower just the TA, then you follow the procedure described in this post since it is the combination of acid addition AND aeration of the water that lowers the TA without also lowering the pH.

The pH only naturally rises if using hypochlorite sources of chlorine. In Trichlor pools, the pH typically drops and pH Up (or equivalent) needs to be added and the TA should be kept higher as well. In pools using hypochlorite sources of chlorine, the rate of pH rise can be minimized by having the TA be lower and targeting a slightly higher pH. Pools and spas are intentionally over-carbonated, partly for a pH buffer and partly (in plaster pools) to saturate the water with calcium carbonate to protect plaster.

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