If you're using 6% bleach, 1.5 gallons is only going to raise your Cl by 7.5 ppm, which isn't high enough to achieve effective shock levels even with 0 CYA. If you have 0 CYA, you're going to need 2.5 gallons to get up to 12 ppm, and if you have CYA of 30, you'll need 3 gallons. May be why you're having trouble with algae wanting to grow....

Janet