Never had this happen before

[Charlie_R]

Had an "unscheduled" rain event last evening, just before my usual testing time. I say unscheduled, because the storm moved in sooner and faster than predicted.

I've been running my FC level where it seems to be most stable, between 4.5 and 5.5. CYA is at ~35 (1/3 below the 30 mark).

Did my testing this morning, and contrary to what had become the norm, pH didn't move, but FC went what I would consider way down. This morning's test showed 2.5 first test, and 3.0 on verification test. 0 CC on both tests.

Added bleach, will retest later.

Rain added about 1" of water to the pool. I've never had that much of a drop in FC due to rain. Usually the pH jumps from 7.4 to 7.8 or better. May have been something odd about what the rain washed off the trees? There is a large amount of dust that has piled up on the bottom now, slightly more than normal.

I'll be monitoring the water closely today, and be prepared to raise to shock level if needed

Just thought I'd try to get a little input from more experienced folks here.

 

[duraleigh]

A big storm introduces some unpredictability so I would say your results are fairly typical. Organics blowing into the pool could account for that FC loss.

I doubt you will need to shock but I think I would elevate the FC a few more points than normal over the next 24 hours to clear up what little might be lingering.

My pH NEVER moves as a result of rain. I would say most pools will experience little to no pH movement.

 

[Charlie_R]

Thanks for that, Duraleigh.

About the pH movement. This effect has been getting less noticeable than when I first filled the pool 6 weeks ago. The first storm after filling, the pH went from 7.2 after adjustment to >8.0. Took quite a bit of MA to bring it down (didn't keep track, just add, test, add, test ad infintum).

Each subsequent storm has move it in decreasing amounts. The next rain event moved it from ~7.3 to just under 8.0.

This is the type of movement I've been dealing with. Maybe Chem Geek could help explain? I'm at a loss as to why it would do this, other than dilution and aeration.

 

[JasonLion]

You didn't post your chemical levels, so I have to guess. It sounds like your TA started high, and the rain provided aeration, raising the PH. Each subsequent time the TA would be lower (from the acid additions) so the effect would be smaller.

 

[Charlie_R]

Sorry, I should know better. Thanks for the reminder.

Opening numbers, after using trichlor pucks:

FC - 7.5
CC - 0
pH - 7.6 - with continued adjustment while pucks dissolved. Tap water normal.
TA - 180
CH - 160
CYA - 40+

Current:

FC - 6.5
CC - 0
pH - 7.4
TA - 120
CH - 140 ?? testing error? or rain?
CYA - ~ 35 (1/3 below 30 mark)

Note: I've had to pump out about 6" of water total due to rain influx.

 

[chem geek]

Yup. Jason nailed it.