Is it best to empty above ground pool water filled with algae or chemically treat it or both?

I had the same problem with my pool. Its 1800 gallons. I changed and cleaned the filter. Then i went and bought a shock treatment to clear the water. You'll have to scrub the sides and bottom with a brush. Then most likely have to change the filtyer again because of all the algae. This depends on how much there is. Also you'll need to use your' skimmer alot and try and get as much alge out yourself so you don't damage the pump. If it's really bad drain it clean it and replace the filter or clean it if you can. I was able to save my without draining it. The filter was just dirty and the pump stopped working correctly. Good luck dude.