CYA too high

[Moniyque]

Above ground pool 10,000 gallon pool. When opening the pool I emptied to only a few inches of water left and filled with new water. Measured CYA and it was 40. Balanced all chemicals and had pool open for about a month. Using tablets in an automated chlorination system set at 4 which maintains the FC around 4. Shocked once with one packet of Dichlor shock (not slam, just regular shock). I just tested the CYA again and it’s 100. What could be causing it to go so high in such a short amount of time?

P.S. I am aware of the recommendations in this group to keep the FC level higher and not shock.

 

[duraleigh]

The use of tablets (about 33% CYA) and dichlor (even higher percentage) has driven your CYA too high. Stop using both immediately and drain/refill half your pool to get CYA in the 50 ppm range. Use liquid chlorine only and your CYA will no longer rise.

 

[AK-]

Each 8oz 3” Trichlor tablet will increase your CYA by 3.3.
Each 1lb of Dichlor shock will increase your CYA by 6