If the CYA was 100+ a few years ago and you have continued to use trichlor pucks, your CYA must be through the roof! You can do a partial drain and refill and try and lower it. Depending on how high that CYA actually is, it is hard to tell what it will be after you drain some. It might take a couple of partial drains and refills to get it to a more manageable level. You can probably drain 2/3 of it at at time. You might try using Poconos' plastic sheet method for draining where you lay a large piece of thick plastic on the top of the pool and simultaneously drain from the bottom as you fill on the top. This might actually be a good idea since it would essentially allow you to completely drain this pool without fear of it popping out of the ground. I'm going to ask Al (Poconos) to come and talk to you about this further.