You do have to get your ph up - anything under 7.0 is corosive, and can ruin your liner. I would add a little borax to get it to at least 7 to 7.2. The chlorine will be just as strong there. You can also aerate your water so it will lower the alk and raise the ph. You are testing no metals because all of the metals are binded with the sequestering agent. You can now shock the pool. You have to be consistant, if you let the chlorine level yo yo, it will take much longer to clear the pool. Get the ph up that is the priority.