Replacing Neptune Optical Sensor

Chuck_e · Mar 14, 2026

Well, don’t I feel silly. This was a rant about replacing optical sensors in the Neptune ATK mount. Turns out I was wrong. I’d delete the post if I could figure out how…

Reefer Matt · Mar 17, 2026

Chuck_e said:
Well, don’t I feel silly. This was a rant about replacing optical sensors in the Neptune ATK mount. Turns out I was wrong. I’d delete the post if I could figure out how…

Don’t feel silly at all, you just learned something. Please share with is what it was.

Chuck_e · Mar 17, 2026

Reefer Matt said:
Chuck_e said:

Well, don’t I feel silly. This was a rant about replacing optical sensors in the Neptune ATK mount. Turns out I was wrong. I’d delete the post if I could figure out how…

Click to expand...

Don’t feel silly at all, you just learned something. Please share with is what it was.

OK, if you insist. I purchased a new optical sensor some time ago as a "critical spare" so I would have one on-hand in case one of the ATK sensors stopped working. I bought the one without the magnetic mount. Well, those of you who know Murphy's Law also know that Murphy was an optimist, and the need arose this weekend. My intent was to mount the new sensor in the Neptune ATK sensor mount, but the sensor didn't stick far enough out the back and so the nut wouldn't bite. After coming up with a workaround that is rather ingenious, if I do say so myself, I read the package and saw the words "silicon washer included". Which I never actually saw. Leading me to conclude that the washer is actually set onto the sensor, and that was what was preventing the sensor from sticking out the back of the mount.

Now, I haven't gone back into the sump to actually confirm that, but I'm pretty sure that's what's going on.

The workaround was to set the sensor into the hole in the ATK mount that the tube from the pump is supposed to be set into. But I don't use that and have the tube discharging into the sump above the high-water level so that there's no siphon. So the mounting hole and more importantly the thumb screw worked perfectly to secure the new sensor.

So yes, I learned something - not sure exactly what, certainly never expected a washer to be part of the package!

I told you it was silly...