pH 6.8 or less is a problem in the "FIX IT NOW" category. It will damage plastic and metal. Go to Wall Mart or the grocery store and buy at least two boxes of 20 Mule Team Borax (in the laundry aisle). While you're there, pick up a few bottle of plain, unscented, bleach. If you go to Wall Mart, see if they have the HTH 6-way drops based testkit (pool section), if they do, buy one.

Go get the Borax ASAP.

Pour 1/4 to 1/2 box slowly in the pool and stir it up as best as you can with a surface skimmer or paddle or wahtever you have. Add a cup of bleach as well. Run the pump and let it mix for an hour or two then test pH and chlorine again.

If pH is below 7.4, repeat the Borax application. If chlorine is below 2 repeat bleach application.

Let us know what's happening.