What is needed for green water in swimming pools and how do I keep it in control without spending a lot of money?

I just went through this last week...you need to get some allgy (?) remover, keep you pool chemicals in check. Mine were way off, almost "dead" water. Also it rained alot and that turnes your water real fast. I did invest in a Pool rover. My pool is big so it was worth it. he keeps my walls and floor clean which is what turned the water. if you keep up with it then it won't cost you a ton of money You need to pick a cleaning/ filter system. There are several, including chlorine, or salt. Best head down to your nearest pool shop for a quote based on the size of your pool and how often you use it. They can give you things like acidity regulators too if you want to go all out.