I was reading you post a bit more closely and I see you have a tablet feeder. How long have you been using it? Do you do regular water draining and refill?

I ask because trichlor tablets add a lot of CYA (stabilizer) to your water over time and, without regular water exchanges, you can easily build up CYA in your water over 100ppm. If I were you, I would retest your CYA again but do dilution testing. Take a sample of pool water and dilute it 1:1 with DISTILLED water. Test your CYA and then multiply the results by 2. If you need further dilution, you can take 1 part pool water and add it to 3 parts distilled water, test CYA and multiply by 4.

The CYA test is tricky and it can be interfered with by high FC or pH out of normal ranges. It's also best to allow the water sample to come up to room temperature if the pool water is cold as the CYA test should be performed on water that is at least 68F-70F.

During a shocking procedure to remove algae, you need to get all of the tricolor tablets out of the feeder. The extra CYA is not helping you. Long term, I think you need to ditch the trichlor tablets and just use bleach in your pool as the stabilized chlorine products just cause more trouble then they are worth. But that's a conversation for another day.