I know, but not as deadly or residual to bacteria as many others chemical like Truban to kill the black mold. After flushing well for a couple of hours, i re-cultured the bacteria and it is alive and well. The system is set up so the water recycles in a closed loop.

I'm thinking that the amount of sodium bicarbonate being used just to adjust the pH is small enough to not introduce enough sodium to be harmful. As a higher concentration it could be toxic, but at the low levels in question, probably much less so. As with many things, the dose makes the poison.