Help with pH please!

[Suzy Shark]

The pH reading of my facility's hot tub has been yellow for the past week. We thought the acid injector might have been siphonning acid out of the vat and into the hot tub; so we changed the injector and then pulled the line out of the vat. But nothing - pH still yellow. We tried to balance it but our CH and TA readings were way off. I have tried adding soda ash, but there is no change in the readings.
Chlorne at 0.0ppm and pH is very much below 6.8.
Any suggestions and/or insight would be greatly appreciated.

[chem geek]

If the TA test turns red immediately instead of initially turning green and then adding drops to turn it red, then your pH may be below 4.5 which is very low. Add more soda ash -- you may not have added enough.