I have been having a problem over the past few years where the water in my pool has a green powder like substance. I have shut the filter off and it settles to the bottom. I have flocked the pool and vacuumed on waste and it comes back every year! All chemicals are balanced and there are no phosphates in the water. I replaced the sand in my filter with Zeo Sand, but can't seem to clear this problem up once and for all. Considering draining the pool this spring, but have read if I do so, with the liner being more than a few years old, it may crack.