Most people selling anything to do with the black tank are taking through the wrong end of the alimentary canal.. that is their words belong in said black tank. The sensors will work.. when the tank is new or when it's been completly cleaned. in short one time.. If you want sensors that work google SEE-LEVEL (With the hyphen) ther are other types of sensors that work better. I never did get around to testing HORST.. planned on it but it never happened. Horst is a "Traditional" sensor that works with your existing panel but is supposed to be more immune to "Sliming".
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The stuff WILL break down, no matter if you add $$$ chemicals or not.. Best chemical to use in your tank is water.