Tunze 3155 ATO with issue

[Ioncewaslegend]

Everything works on this ATO... Sometimes. The optical sensor seems to be on the fritz with no rhyme or reason when it decides to not detect low water. I've tried soaking it in vinegar and cleaning it, but no luck.

Don't really want to send it in to be fixed, and want to pick up a HR nitrate checker, so trading for a hr nitrate checker, Neptune AFS, or $55. Located in San Jose, CA.