Hello, and welcome to the forum!

If you use a chlorinator, then odds are really good that your CYA was high at closing, and the algae outbreak that happened over the winter biodegraded the CYA. When that happens, one of the possible by-products is ammonia, which will create a HUGE chlorine demand. We've seen lots of cases of this, but never more than we have this year, and I think it's mostly due to the unseasonably warm winter.

At any rate, what you need to do, whether it's ammonia or not, is to shock the pool by bringing your chlorine level up to 20 ppm and holding it there as consistently as possible until the algae that you see is gone, and until you can go from sundown one evening to sunup the next morning without losing more than 1 ppm of chlorine. If you have ammonia in the pool, this may take awhile, but that chlorine demand needs to be overcome before closing, otherwise you'll have a real mess on your hands next year. Test as often as possible, and add more chlorine to get back up over that 20 ppm mark, because the more consistely you hold it at shock level, the faster the demand will be overcome. 2.8 gallons of bleach in 27K gallons is only raising your chlorine by just over 6 ppm, so that's not nearly high enough to kill off anything growing in the water. In fact, with a CYA of 75, your minimum chlorine level should be 5 ppm.

I would use bleach for the shocking--if you turn the chlorinator up, you probably still won't be able to achieve 20 ppm all at one time, and you're just raising your CYA higher--which in turn will require you to maintain your chlorine higher.