The TA test should go from green to red or sometimes blue to yellow (have you used any non-chlorine shock?) so I'm not sure that gray means there is low TA. Did you add any of the reagent to see if there was a color change from the gray? I don't mean to insult you, but have you checked to make sure that you're adding the right reagents and how old are they? Have you tried checking the TA of your fill water to see if you get the same result?

I've never had it turn gray or black, but I'm still not convinced that just means the TA is low......

And yes, if you can divert the water away from the heater, I would until you get the pH and TA straightened out.........

Janet