Does pool water get stale? I have constant ALK drops and PH increases

[keithw]

I have a 6K gallon fiberglass pool. Have had the same water other than rain and top ups for many many years. Never done a full drain. I chlorinate with bleach (Liquidator). I keep all my numbers pretty perfect. TA 110ish, PH 7.4, CYA 40-50, CL 4-6.

Starting about 2 years ago I developed this ALK decrease, PH increase issue. I would say I lose 10PPM ALK per week and PH prob goes from 7.4 to 8.3 each week. Also had a wild scale outbreak earlier this summer that I had to sand off the pool. Water looks perfect right now other than the two creeping chemmies that I mentioned.

Haven't changed my pool filter sand in about 5 yrs. Was planning to do it this fall.

Any ideas? Normal? Does water just get stale after awhile? Considering doing a 3/4 drain and refill this fall.

 

[JamesW]

The problem is that you're keeping the TA too high and the pH too low. The combination creates excess CO2, which causes ph rise. When the ph rises, you add acid to lower the ph, but that also lowers the TA, so you add bicarb and the cyle begins again.

Try TA at 60 and ph at 7.8.

NaHCO3 + HCl <> NaCl + CO2 + H2O

Sodium bicarbonate + hydrochloric acid = salt + carbon dioxide + water.

 

[keithw]

Isn't 60 low? I have always tried to keep TA around 100. Used to be able to keep it there too. But not anymore.

 

[JamesW]

The best TA is whatever keeps your pH stable. If your ph keeps going too high, your ta is too high. If your ph keeps going too low, your ta is too low. When the ta is right for your pool, the ph will be very stable.

Try TA at 80 and ph at 7.8. If the ph keeps going too high, lower the ta again.

 

[YippeeSkippy]

Don't bother changing your sand out- it never wears out in your lifetime and only rarely needs changing (such as converting a pool from Bacqua to Chlorine).