Since your pH is at the lowest your kit will register, it's a good bet that it's actually a lot lower. I would start with about 2-3 cups of borax added very slowly through the skimmer with the pump running, give it 2-3 hours to circulate, then retest and add more as needed to get the pH up above 7.0. Depending on how low your pH actually is, it can take large amounts of Borax!!

Your TA might move slightly, or might not move at all--but the pH is the more critical of the problems right now, so fix that first, then deal with TA.

Janet