Ok, I've done some research on the products you're using. The clarathon hose filter looks to be just a pleat filter, so no prob there, in fact it'll help you in the long run when adding fill water. The Banish algaecide does contain copper (attached MSDS), but unless you have used a tremendous amount quite recently, it shouldn't be affecting your water like this. In the future though, I would not recommend using any copper based algaecides. They are effective against algae, but can be harmful to the environment, especially if you you are back washing and dumping it somewhere. It's a known toxin to fish and aquatics. The only product I would recommend in the future is a poly-based algaecide, I have attached a photo of the one I use on a weekly basis. They are made by many companies, so you'll most likely find it at your pool store. Could be under the names of of Polyquat, Algaecide 60, Algea Destroyer, etc. You'll have to look at the label to make sure the ingredients are the same as the one I posted. All algeacides, however, are only good as a preventative, so it'll be something to consider once we get you cleared up. Since we don't have any obvious sources of large amounts of metals entering the pool, I have to believe you have just come across a stubborn algae bloom. You're just going to have to keep at it, and eventually it will clear up. As far as, draining the pool, there can be problems when draining an above ground pool 100%. Depending on how your pool was built, and the surrounding land (i.e. embankments, slopes and hills), a cave in could be possible without any water to support it. If anything I would drain no more than 50% of the water to be on the safe side. Also, there could be issues with the liner with no water in the pool. Draining the water now would not help your current algae problem, in fact, it may make it worse. You'll be diluting the algae, but, also the chlorine. You also would not be able to circulate the water, while refilling, giving the algae time to grow again, without the proper amount of chlorine in the water.
lol
