Spa pH keeps dropping??

[DigitallyChallenged]

My spa is plaster, 750 gallons separate from pool filter system. All of a sudden the pH keeps dropping to the 6.9/7 level frequently. I have not been using spa due to the heat. I use chlorine and this has also started to run quite low. TA 90, CH 275. Borates 35

I have been running air pump to boost pH but this is transient. Added some Borax and this also has been a transient response. My FC has been from 0-3 using an inline chlorinator. I have been adding bleach to raise FC as needed. Water looks fine, no algae.

What would cai=use this all of a sudden and how should I deal with pH and FC?

 

[jblizzle]

How are you adding chlorine? I see "auto chlorinator" listed for your spa.
If you are using trichlor tablets, they are acidic and will lower the pH and TA, as well as raising the CYA.

 

[DigitallyChallenged]

I have been using tablets. Would soda ash correct the problem?

 

[jblizzle]

Depends on all your test results, but basically no. The tablets will continue to drive the pH and TA down.

You can try raising the TA up to 120ppm or so with baking soda which might slow the pH drop some. But, are you also keeping an eye on the CYA level and keeping the FC adequate for it according to the [FC/CYA][/FC/CYA]?

 

[DigitallyChallenged]

My CYA has always been on the low side and I have been using the chart. I only run my pump for 3-4 hours a day for the past year and this has not been an issue until now.

 

[jblizzle]

Well, perhaps the TA has now been driven low enough that the pH is more influenced by the tablets

Bump it up.