I built a 275 gallon pond (flex liner) 3 years ago. No fish, it's only 14" deep, and it's in full sun so the algae problem is awful. I have a Pondmaster MagDrive 700 gal/hr. pump with a tiny "prefilter" and no skimmer or any other equipment (PUMP ONLY.) The pump just sends water through tubes over the rocks above the pool. The water turns green in just a few days. I've added bleach and I've tried "pool shock" for swimming pools without success. WITHOUT STARTING OVER, what equipment can I add or what can I do to keep the water clear?