Start by taking a snapshot of the water with Ben's test kit. Then correct from there. You'll probably want to shock your pool up to the max for your stabilizer levels, and keep it there while you clean out the winter junk (leaves, pollen, bugs, etc) and get your water clear. Once it's clean and will hold a chlorine level (CC=0 usually), you can add polyquat. It won't hurt and it can help. See my other post in this forum.
I suspect you are keeping your FC level too low for your stabilizer level, and therefore you are getting blooms. Are you using bleach or powders/tablets for chlorination? Di-chlor powder and Tri-chlor tabs add stabilizer and can take you FAR higher than you realize. If your stabilizer level (CYA) is 100, you simply cannot keep your pool clean with a chlorine level of 3 or 4ppm (for example). I don't know when Ben is going to post the "Best Guess" table again for suggested FC levels for given stabilizer levels--he may already have done so. You need to follow that to keep algae from growing.
Also be aware that chlorine is more effective at the lower end of the suggested pH level than at the upper end. I prefer to keep pH between 7.3 and 7.6 for that reason. 7.7 to 8.0 will make your chlorine less effective. However, higher levels may reduce eye irritation, if it's a problem.
Everything is a balancing act between the choices for what you need.
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