Alkalinity?

[waterbear]

I think I see what the problem is. I just noticed your chlorine levels are well above 5 ppm (bright orange on OTO test!) . If they are very much above about 10 then when you test pH the phenol red indicator is being converted to chlophenol red which is an indicator for a lower pH range! (some indicators are better than others...i.e. have a chlorine neutralizer built in, but this will only work to a point and some conversion of phenol red to chlorphenol red will still occur at high chlorine levels) It is entirely possible that your pH is below 6.0 now if your chlorine levels are very high! the color that chlorphenol red prduces at a pH of about 5.4 is similar to the one that phenol red produces at about 7.2! I suggest that you get your chlorine done at a pool store that uses an FAS-DPD titraton test (or buy such a kit yourself) and find out just how high your clorine level is. If it is above about 10 ppm then you should treat you pH readings as suspect until it drops down.

you will not see a deacrease in alkalinity until the pH starts to climb above about 7.4 so it might take airating for a while, given the low pH.

IMHO, I would not add any more acid right now until the CL levels drop to normal ranges.

First thing is to wait for the CL levels to drop below about 8 ppm and then test the pH. Once you know where it is then you will have a better idea what to do next!