Just getting started and have a chlorine demand problem

[CarlD]

OK, it looks like your FC level is 5, your pH is 6.8 (very low!), your CYA is now 100--very high.
An 12,000 gal AG pool with a 2hp pump? I hope you have a 300# sand filter because it's 'way, 'WAY too big for your pool!

I'm guessing you've been using Tri-chlor tabs and/or Di-Chlor powder because your CYA is very, very high and your pH is low. Both of those types of chlorine add CYA and are super-acidic, driving down pH, especially the tabs. Stop using them.

First: Put a box of 20 Mule Team Borax in your pool TODAY--vinyl pools with pH below 6.9 can be damaged by the acidity.
Next: You have a choice: You can drain 6,000 to 9000 gallons and refill, and lower your CYA to a more manageable 30 to 50ppm. I'd go for 6000, and maintain CYA at 50.
Next: You need a better test kit. We recommend the Taylor K-2006 or 2006C that allows testing of very high chlorine levels.
Next: Check out the Best Guess table for the ratios of CYA levels to chlorine levels. Start with that here: http://poolsolutions.com/gd/best-gue...ine-chart.html
Next: Get us more details on your pump and filter. Brand and model will help and, if you know it, the size of the sand filter, either in pounds of sand used or inches.
Plus a full spectrum of tests of your water:
FC, CC and TC for chlorine
pH
Total Alkalkinty
CYA
Calcium levels,

Just so we know.

Carl

[Watermom]

OOPS. Just noticed your CYA reading used to be 70, but is now 100 which means it could actually be higher than that. So, as Carl said, you might consider doing a partial drain and refill. If you choose not to do that, you'll have to shock to 25 instead of 20 and then when it is all cleared up, your maintenance level is going to be between 8-15 instead of 5-10. Let us know which is your preference and then we'll help you go from there.