Question on rapidly rising pH and falling FC

[Mcas]

Hello all,

I am noticing in my pool (one year old) I am seeing what appears to be quickly climbing pH with quickly depleting FC. Here are my stats as of today.
FC 1.4
pH 7.8
TA 90
CH 250
CYA 50

Here were my stats as of 24 hours ago:
FC 4.2 (this was my measurement several hours after making an adjustment to increase FC)
pH 7.4 (this was my measurement several hours after making an adjustment to lower pH)
TA 90
CH250
CYA 50

I am wondering why my pH is climbing so much within 24 hours and where all my chlorine is going so fast.

I do run a small waterfall for a few hours a day, which can lead to the climbing pH. And I believe I have enough CYA to protect the chlorine against sun degradation.

It's been very hot (104) for a few days and my pool gets a lot of direct sun (9AM-6PM).

Appreciate any help!

 

[mknauss]

You will lose 2-4 ppm FC each day. Keep your FC above minimum at all times.

pH rise is tied to fill water, TA, and aeration. What is the TA of your fill water?

 

[Mcas]

Thanks for your reply.

I saw a thread you posted on how to properly test CYA, and I followed those instructions...utilizing the glance method.
My CYA is 40, not 50. Thinking I might need to bump that up.

I just tested my fill water and the TA is 9 to light pink, 10 to dark red.

 

[mknauss]

So the TA of your fill water is 100. With the evaporation you get, you will have a pH that rises all summer.