Alkalinity Problems

[Illinifan]

Vinyl In-Ground Pool
18500 gallons
DE filter
I have been testing and maintaining water chemistry for several years with absolutely no problems. This year when opening the pool my alkalinity has been very low.
Yesterday, my numbers were as follows:
Free Chlorine 8.10
Total Chlorine 9.51
pH 7.8
alkalinity 42
CH 237
CYA 75

I added 1.8 gallons of 12 % bleach and 15 pound of baking soda.

Today, my numbers are:
Free Chlorine high
Total Chlorine high
pH 8.0
alkalinity 35
CH 257
CYA 75

I obviously need some help here. I am not too worried about the chlorine - the sun will take those numbers down. But the alkalinity/pH have never been this off. I would appreciate any suggestions.
Thank!
Illinifan

 

[ajw22]

Welcome to TFP.

We would like to see tests from your own test kit and not pool store tests. We have found pool store testing is too unreliable to use.

We recommend you get the TF-100 Test Kits or the Taylor K-2006C. See Pool Test Kits - Further Reading

Are you using Trichlor tablets?

 

[Illinifan]

Thanks for your reply. The problem is on the way to being resolved. Those were the tests from my LaMotte ColorQ7 test kit, which I have used successfully for several years. I get new reagents every year. I contacted LaMotte last week and they said that the alkalinity reagent was faulty. They said it tested fine when shipped out but when customers returned it, it tested low. Their vendors were notified, but apparently my supplier either did not get the information or ignored it. A replacement reagent is on the way. I never use pool store testing. I also found it unreliable. I do not use Trichlor and Dichlor, except upon two occasions last summer when we were out of town. All I use is 12% bleach.
My numbers are now approaching acceptable:
FC 4.16
TC 4.20
alkalinity - awaiting new reagent
pH 7.6
CH 208
CYA 70