Why would my TA crash?

[CrisL]

I have a mesh cover and my TA goes to 30 or so every winter, with my ph dropping somewhat, going down to 7.0 to 7.2. Once I bring it up, the TA stays at about 90-100 all summer with no other changes.

[chem geek]

According to this website, in Shrewsbury, MA from December to April it rained about 13" or about a foot. According to this EPA website, normal rain has a pH of around 5.6 (due to carbon dioxide in the atmosphere) while the most acidic acid rain is around 4.3

If your pool has an average depth of 4.5 feet, then one foot of rain would replace 1/4.5 = 22% of your pool water through a process of continuous dilution which is equivalent to a drain/refill of 20%. If you started with a TA of 80 (and a CYA of 30) and a pH of 7.5, then replacing 20% of your pool water with "acid rain" water with a pH of 4.3 means adding 10^(-4.3) moles/liter of hydrogen ion and you would remove up to 20% of the carbonate buffer. So the pool's TA would drop to 64 (due to CYA going to 24) mostly from dilution (not acidity), but the pH would barely drop at all (about 0.02) because even acid rain isn't very acid when added to the pool's "buffered" water.

Rain can certainly cause the TA to go down and the pH to drop, but it would take a lot more rain than one foot. Even replacement of 80% of the water would only have the pH drop down to around 7.2, but after that the pH can drop much more rapidly.

So I still can't explain why you saw such a large drop in TA.

Richard

[Ohm_Boy]

can anyone speculate on why the TA would crash from a normal reading in the late fall

Old reagents?

[TwistyKat]

Thanks for the replies.

We have had a lot of rain (and snow) here over the off-season, but we had a lot last year also and I didn't see the same numbers.

I did replace my reagents but after I already hit the pool with about 16 lbs of baking soda. My TA was at 190 by the next day (with the new reagent) and the PH was 7.9.

I've been hitting the pool with small amounts of Muriatic Acid all week, and I have a small pump tied up in the corner of the pool doing some circulation. It's also breaking the surface of the water to hopefully provide some aeration.

Last night the TA was down to 140 and the PH was down to 7.2.

I guess I can't rule out the the reagents were faulty, but they were new last summer and I keep them in the house during the off-season.

My plan is to get the TA down to 100 then work on bringing the PH up to normal.