Total Alkalinity - why maintain at 80+ ppm if pH stable

Problems relating to pH and total alkalinity.
Increase ph, increase TA. Reduce pH, reduce TA.
pH chemistry advice and techniques for the pool.
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Total Alkalinity - why maintain at 80+ ppm if pH stable

Postby perthWA-RAT » Sat 25 Feb, 2006 02:10

Over many years of maintaining my pool's TA at 80-100ppm this seems to then result in the requirement to constantly add acid (500 to 1000mL) at a time every 3-4 days to maintain pH down at 7.4 - 7.6. Over time TA comes down and then I add buffer to boost TA. If I let TA slide to 65-75ppm and dont add buffer, pH seems to test constant at about 7.4 and no acid required. If I don't get pH "bounce", or low pH, why maintain the higher TA?

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Low total alkalinity

Postby Pool Help » Sat 25 Feb, 2006 06:39

Low total alkalinity can result in eroding of plaster/ gunite pool surfaces. The total alk you mention is not extremely low and may be quite acceptable.

Swimming pool water balance includes several factors, each with its own set of parameters. These are guidelines and one "high" level can offset a "low" level resulting in ideally balanced water.

Assuming a total alk of 65ppm and a pH of 7.5 with a hardness value of 400ppm at 24 degrees C, your pool would be perfectly balanced, resulting in neither scale nor erosion. (Calculation of the Langelier Saturation Index - I have suggested to Larry (site owner) to put a calculator up here for this and he has promised to develop one for the forum users.)

If this were my pool, I wouldn't worry about increasing the total alk. That only results in adding alk-up (sodium bicarb) and then acid to bring the pH down. So you end up chasing your tail. Just make sure the hardness is high enough (at least 200ppm) to offset the corrosive nature of the water
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Low total alkalinity

Postby Larry » Sat 25 Feb, 2006 07:31

Yes Pool Help, I agree.

The individual levels are guides and should be evaluated relative to each other. I rechecked you calculation and found it spot on.

There was one more comment I wanted to make. I found it unusual that the TA keeps falling after the addition of the acid. Perhaps try adding the acid to half a bucket of water and distributing the diluted acid evenly around the pool with the pump running. This way you may prevent the TA from falling as rapidly.

Extended monitoring of the TA is essential to make sure that it does not fall below 65ppm, which is already on the low side. I usually find that once a pool has found its balance, it is relatively easy to maintain the balance using very little chemicals. Its the up-down swing of the levels that consumes unnecessary and expensive pool supplies.

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