PH went from 7.8 to 6.5 in 24 hrs!

[kikipunx]

My PH today came out at 6.5, or lower since that is as low as the test goes! I've never had the occasion where I needed to raise my PH. It's always in the 7.6-7.9 range. I add acid every 1-2 days to keep it there since it tends to creep up to 8+. I add whatever amount Pool Math tells me. Tuesday it was 7.9 & I decided to add a tiny amount to bring it to 7.7. Wednesday it was at 7.8, so I left it alone. Today it is 6.5?! I live in Central FL, we've had no rain in a couple weeks, pool is clean & clear/no debris, I don't use tablets.
Other figures:
FC - 1.5
CC - 0
TA - 90
CH - 300
CYA - 40

My FC had been consistently 1-1.5 ever since the heat started up around April! Pool Math has me add roughly a quart of 10.5% chlorine every day to bring it up to 5.

Any ideas what could have caused the crash in PH so quickly?

Thanks

 

[mknauss]

Only adding acid.
I would retest from another area of the pool.

 

[JamesW]

Probably test error.

Are you using the same container to add acid as you use to get a water sample?

 

[kikipunx]

I tested from 3 different areas of pool, using a different clean cup to get a water sample each time. 6.5 each time.

 

[JamesW]

How much acid did you use recently?

 

[JamesW]

Wednesday it was at 7.8, so I left it alone. Today it is 6.5?!

It was 7.8, and you did not add anything, and now it's 6.5?

What was the TA then and now?

 

[JamesW]

Pool Math has me add roughly a quart of 10.5% chlorine every day to bring it up to 5.

Any chance that you added from the acid container thinking it was liquid chlorine?

 

[kikipunx]

The last time I added acid was Tuesday night - only 3 oz. I keep chlorine & acid in different rooms & the containers are very different looking, so no possibility I mixed them up. TA was 80-85ish on Tues & Wed. 85-90ish tonight.

 

[JamesW]

The numbers make no sense.

I would get a different bottle of pH reagent and retest.