Hi, Doug.
If it were my pool, yes, I would ditch the chlorine feeder and just use bleach. You really don't want a CYA reading higher than 75. Can't really predict how often you would need to add bleach although the good part of having a higher CYA like you do is that it allows you to go a little longer between additions of bleach.

Take a look at the Best Guess Chlorine Chart in my signature below. It gives you the minimum and maximum chlorine levels you need based on your CYA reading. Test every day for awhile and you will soon discover how often you need to add bleach to keep from ever going below your minimum. On the days you do add bleach, add enough to get to your maximum. After awhile, you will learn how your pool behaves and how many days you can go between doses to keep your chlorine level in range.

I think your volume may be a little more like 25,600 gallons. In a pool this size, each 121 oz. bottle of 8.25% bleach will add approximately 3ppm of chlorine. Use that as a reference when deciding on doses. (By the way, what kind of test kit do you have? I'm hoping it is a Taylor K2006 since your CYA is high. I'm assuming it must be since you were able to measure a chlorine reading of 12ppm.)

As far as opening to a chlorine reading of 12, well, I think you are just lucky!

Welcome to the Pool Forum. Let us know if you have any more questions.

Edit -- upon rereading your post, I noticed that you didn't list a pH reading. Do you know what it is?