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Continuously Low Ta Level


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This is a 10,000 gal a/g pool in its first season.

The pH maintains well at 7.4. Sanitizer is trichlor pucks inline with the sand filter. CYA is mostly at 30-50, never higher though sometimes the strip reads below 30. FC and TC readings are stable at between 1 and 3. TH has never been above 100 but I've never added any muriatic acid or other such hardness increaser. I occasionally shock with liquid chlorine.

The total alkalinity ranges between 80 and 120 and I've been told by both the installer and the pool store that for a vinyl a/g pool the TA should be at 150. I keep adding Alk-Up but the alk doesn't go up. What the heck am I doing wrong???

I don't understand WHY the alkalinity should be at 150; what does it do to the liner and/or equipment if it's too low? The same question applies to total hardness.

Waterbear, if you're reading this, could you give us some input?

Oh, and P.S.: can I just get Arm & Hammer baking soda at Sam's Club? That would be a whole lot cheaper than the pool store product.

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This is a 10,000 gal a/g pool in its first season.

The pH maintains well at 7.4. Sanitizer is trichlor pucks inline with the sand filter. CYA is mostly at 30-50, never higher though sometimes the strip reads below 30. FC and TC readings are stable at between 1 and 3. TH has never been above 100 but I've never added any muriatic acid or other such hardness increaser.

Muriatic acid is used to lower pH. Calcium chloride is used to increase hardness.

I occasionally shock with liquid chlorine.

The total alkalinity ranges between 80 and 120 and I've been told by both the installer and the pool store that for a vinyl a/g pool the TA should be at 150. I keep adding Alk-Up but the alk doesn't go up. What the heck am I doing wrong???

The trichlor you are using is acidic and could be the reason your TA is not rising. I suspect the problem is with the strips. They do not have the precision you need to make adjustments.

I don't understand WHY the alkalinity should be at 150; what does it do to the liner and/or equipment if it's too low? The same question applies to total hardness.

Don;'t really know for sure but I suspect it is because the vinyl liner is leaching acidic compounds into the water. I have never seen this documented but I suspect this is what happens. The higher TA will help keep the pH stable longer.

Waterbear, if you're reading this, could you give us some input?

First thing, ditch the strips and get a drop based test kit. Walmart has one for under $20 that is decent (but it only tests TC and the Cal test has some issues) If you want to get a good kit get the Taylor K-2006 (NOT K-2005). This will solve a lot of your testing problems. Test strips just don't have the precision for making chemical adjustments!

Oh, and P.S.: can I just get Arm & Hammer baking soda at Sam's Club? That would be a whole lot cheaper than the pool store product.

Baking soda is EXACTLY the same chemical as alkalinity increaser! It is what you need to be using to raise the TA but you need to be testing with a drop based kit and not strips to do it!

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Baking soda is EXACTLY the same chemical as alkalinity increaser! It is what you need to be using to raise the TA but you need to be testing with a drop based kit and not strips to do it!

I do also use a reagent kit, primarily to make sure of the pH, and the TA levels agree with each other to within 10 point. The strip might read 80 and the titration will read 90.

It did occur to me today though that a pool is not a static system. It's essentially a buffer solution and each time I add a chemical I change the balance of the other chemicals. Maybe I just never have added enough sodium bicarbonate. I tend to be on the conservative side with chemical additions.

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I do also use a reagent kit, primarily to make sure of the pH, and the TA levels agree with each other to within 10 point. The strip might read 80 and the titration will read 90.

It did occur to me today though that a pool is not a static system. It's essentially a buffer solution and each time I add a chemical I change the balance of the other chemicals. Maybe I just never have added enough sodium bicarbonate. I tend to be on the conservative side with chemical additions.

when you add the sodium bicarbonate it will raise the pH....this is normal...You want the TA to be a bit higher than your target because one you get the pH back in line the TA will move down with it and should be right on target then.

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