ATO reversed flow

[Ranchu50]

Hi all,

I’ve recently had my Tunze nano ATO act up on me.

After i turned off the pumps to feed the fish, and then turning back the pumps on, the water somehow reversed its flow today, subsequently flooding my rodi water resevoir bucket.
I caught it quickly and turned off the ATO . Minimal damage done ...just a wipe with a couple towels.

Has anyone had this happen?

I have a RSM 250 and the ATO pours the water into the back sump.

The water tube was touching the water in the back chamber when i turned off the pumps.... is this the cause?