I, personally, never have.
I have two Aqueon Pro's and the instructions specifically say that they automatically shut off if they sense that the water level has fallen, how they do that, I don't know.
Long story short, I just had one of them crack after two years of reliable service and I'm wondering if that might be part of the reason. I don't know if the light shut turn off when the water level drops or how low it has to drop to trigger a shut off, but when I do PWCs, the lights on mine always stay on. Maybe they're off, but the lights stay on, maybe the water has to fall lower, maybe it has to be low for longer than the 15 minutes it takes me to do the change (my guess).
I've read other threads from people that say they turn their heaters off, regardless of what's said, like it's the law. Part of my fear is that I won't remember to do it. My plan is to leave my light on one power strip and my heaters and filters on another so I can flip one switch to turn them all off during water changes. The filters are easy to remember to turn back on (since I can hear them and one of them is HOB
so I have to prime it).
Also, just a word about Aqueon (also the makers of All Glass). I was going to order another one, but I called them this morning and, no questions asked, they just told me to send it in and they'd get another one out to me right away. On top of that, I live very close to them so I just dropped it off (but they still have to mail the new one, which they said would happen this week), so that shaved a day or two off the process.
I'm glad I run two of them all the time. It's a 40g tank. I have one 150w heater and one 100W. The 150w heater is the one that cracked and the remaining 100w seems to be having no problem keeping the tank warm. The fact that ambient temperature in the house has been well over 70, I'm sure, is helping quite a bit.
I'm also glad I caught it before anything really bad happened. I heard a very quiet hissing noise in my house. It wasn't my computer or the TV, not the water heater (for the house) or the AC
or furnace. I finally tracked it down to the aquarium. I was terrified that it might have sprung a leak, but I didn't see any water. Unplugging the filters didn't stop the noise, but I still couldn't place it. Over the next few hours I noticed the red light never turned off so I unplugged that heater and pulled it out to find a big crack on it. The hissing must have been water getting in and boiling off (then building up pressure and hissing back through the crack). The entire setup is plugged into a GFI, but still.
So, I'm sort of curious if it cracked because I don't turn it off during water changes and it over heated or it was just a fluke.
R. do you unplug your heaters during PWCs? What if the manual specifically says that they turn off if the water level falls?