Yes, it is possible to have a cya > 100. The cya test is the hardest test to read. Try it again and see what you get. If you have been using trichlor tabs for a long time, it may very well be over 100. If that is the case, if it were my pool, I'd do a partial drain and refill. (probably about half the water which would take your cya down to 50 and would be much more manageable.)

Alk and pH are ok.

Also, do shock the pool. How does the water look?