CL: .5-1
PH: 8.2
TA: 10000
CH: 2500
CYA: 55

20000 gallon plaster
Trying to close my pool tomorrow. I haven't backwashed for a few weeks. Should I backwash and add some DE before close. See my ph is to high what should I use.

Use Muriatic Acid to bring down your pH. I am sure others will be along to help you out a little more.

How did you get those test results? TA can't possibly be 10,000, and CH at 2,500 seems rather unlikely. That makes me suspect the other results as well.

If your PH is really 8.2, you need to bring it down to around 7.2 before closing.

You should backwash the filter right before closing and then turn off the pump without adding any more DE. After closing you should open up the filter and do a through cleaning.

Alk is 100ppm
CH is 250ppm
Have the TF-100 test kit.
If I use muriatic acid won't that lower my alk where my alkalinity is right where it needs to be?

Acid does lower the TA, but not usually by all that much. The recommended TA levels are either 60-80 (SWG) or 70-90 (otherwise), so lowering TA is probably a good idea. In any case keeping the PH right is a much higher priority than keeping TA right. Get the PH to where it should be and then adjust TA if needed.

I have found for me 90 for TA is a good fit.