Chances are that the Borax hasn't yet made a difference because your ph is reading at the lowest level on your tester--but is actually much lower than that! It can take lots and lots of Borax, but you need to get that pH up.

Trichlor tabs are very acidic and will drive your pH down. Check the ingredients on that powder shock you're using, too--if it's sodium dichloro.....(lots more syllables), then it is also part of why your pH is so low. AS Watermom said, you need to get that pH up above 7.0, ASAP--before your liner is shot.

Janet