This is the best video I have ever seen on black tank, really any tank maintenance.
https://youtu.be/fs7YE9hmD7k?t=3159
That link will take you to where the company owner talks about what they recommend for tank treatment, (and he gives the "recipe" away!) but if you have time you should really watch the whole video.
Somewhere in it he says where people mess up with tanks is by treating them like septic tanks. They are not. They are holding tanks, and are not put there for the purpose of digesting waste products. That is counter productive if you want to keep your tanks clean and your monitor probes working.
Last season I started just using plain water... lots of it in the black tank and never had an odor problem, and never had any issue dumping. I was really surprised. This season I plan on mixing up a batch if his "solution" and giving it a try, especially in the gray tanks where we really don't have the need, or the capacity for extra water on board.
Long video if you watch the whole thing, but great information from someone who has cleaned hundreds of RV tanks in his business and I assume he knows what works and more importantly, what doesn't.