Perhaps this constant on/off and the resulting TDS creep is why Im eating through DI resin so quickly too... (besides the idiotic accidental reversal of 1 and 5 micron carbon blocks 6 months ago or so)

hmm.. this float switch thing sounds similar to my DIY ATO except wired differently.. or with a different relay..

im racking my brain on how the switches would have to be done, or which kind of relay used to make this work... Do you mind sharing the parts you used to put it together, or a source for a completed setup?

Thanks