We have the same kind of pool and we got a big blue tarp to keep over it, anchoring the sides with bricks. It works pretty well. And I use nearly all the water to water the plants. When I change the water (once a week or so) I scrub the inside with a little clorox spray and then rinse it out. We still get a little slime, but this works pretty well. And the scrubbing sounds like a pain, but it really isn't all that bad - only takes about 10 minutes.