I noticed that even keeping chlorine level @ 6-7 ppms my water eventually begins to turn green. I been maintiaing water clear with algaecide called skill-it. I use 7 oz per week. I also got some oxidising shock to give it a boost and my question is that since the oxidizing shck is chlorine free, how would one measure if you reached shocking level as you would normally determine with a kit for chlori ne?