I have no idea if grout affects pH or not but I do know that low pH will destroy pool equipment as is evidenced by your heater! If your copper in your heat exchanger has corroded, you unfortunately now have another problem as well --- metals in the water. It is copper and not chlorine that stains things and turns blonde hair green.
You need to add some 20 Mule Team Borax (laundry aisle at Walmart) to bring your pH up. Any reading below 7.0 is acidic and will as you have found out, damage your pool and/or equipment. Add a third of a box slowly to the skimmer while the pump is running, breaking up any clumps. After a couple of hours retest pH.
You've got a mess on your hands. I'm going to ask Ben to have a look at your post.
Welcome to the Pool Forum, by the way!
(p.s. I'd fire the pool company. They obviously don't have a clue what they are doing.)
Bookmarks