I think your first step is to pass OCLT...Overnight Chlorine Loss Test. You should not lose more than 1 ppm chlorine overnight, and you should not have greater than .5 CC. Measure at night before you go to bed, and in the morning before the sun hits the pool. For instance: If you go to be and FC's were at 15. When you woke up and measured...they were at 13...you have failed the OCLT, and need to continue shocking, because something in your pool is still consuming chlorine. Actually the chlorine is fighting something and being lost.
Step 2: Get your TA down with Acid/Aeration (after you pass OCLT). Mine was 250, it took me 2 weeks, but I got it down to 80 now.
Step 3: Get your CYA up to maybe 50 or so. I understand you already added CYA, but you won't get an accurate reading on the test until about a week after it dissolved. So don't mess with that for awhile. (You can deal with this even if you're still shocking).....so this could actually be step 2.....depending on whether or not you pass OCLT quickly and can drop to normal FC levels.
My guess is with your high CYA's from last year, the 7ppm of FC you were keeping was allowing algae to grow in your pool. It may not have been visible or causing problems, but it was there, and was definitely consuming your chlorine. Now that your CYA will be inline, you will be golden.