If you are using liquid chlorine you do not need to test CYA every week. The only way it is going to change is if you add cya or by adding a bunch of water. Once it's in the pool it really only lowers by dilution. I only test my CYA about once a month or if I get several inches of rain.
Yes, if you continually add stabilizer you are going to have problems. That is the entire problem with using chlorine tablets or powder shock, it adds stabilizer with every dose. The stabilizer builds up and eventually reaches a level so high you can't reasonably add enough chlorine to keep the algae away.
If your CYA level is moving up and down between tests it's likely a testing error. Maybe
this video will help, from another post I think you have a K-2006.
At a CYA of 50 you need FC of 4ppm minimum. You should be dosing your FC up to about 7ppm, that way as the chlorine is consumed through the day FC can stay at or above your minimum. It's best to test every day at about the same time, then add your daily dose, enough to reach your target level of 7ppm. The next day when you test near the same time of day, you should be at or above your minimum of 4ppm. I test and dose in the evening, that way the FC remains at higher strength for the most hours per day.
You are either not adding enough chlorine or you have something consuming it. Try adding your chlorine dose, let the pool circulate for 30 minutes and test again. Using 8.25% bleach it should take about 56oz to get from 2ppm up to 7ppm in a 7600 gallon pool.
Have you checked the label on your bleach to confirm the strength? Don't know where you get your chlorine but places like the dollar store have very weak bleach, often down around 3%.
