Looking for ideas to improve fish tank ATO (Auto Top Off)

Hi all,

I have a small reef tank (Red Sea Reefer 170) and the ATO that comes with it is mechanical float-based... its junk so I replaced with a optical-sensor based ATO that works real well - but the fresh water reserve only holds about a gallon... when it runs out the ATO will shut off so the pump doesn't burn out and start beeping to let you know it's run dry.

Once the fresh water is replenished the ATO needs to be reset by power cycling it - so I've found the most convenient way to do this is to use a z-wave on/off plug. I called it "fish tank" and I just say Alexa turn off fish tank... refill the reservoir when I get a chance and then say Alexa turn on fish tank to reset.

It works pretty good, but here's the thing... if I am not home the thing just beeps forever and I would prefer not to torture the other pets in the house. So - I am looking for some suggestions as to how I might automate turning it off? I would then just use notifications to alert me.

I've seen there are some sound sensors but they appear to be geared toward fire-alarms (this isn't loud enough) so I am thinking I might need to get a relay and "something?" else


If you know the general refill rate you need to perform (it runs out every week for example, or every 10 days) you could set a Rule to shut it off after 7 (or 10, or whatever) days. Not perfect but it does not require you to get anything extra.

I am a bit spoiled on this though since I use a Neptune Apex and have it all linked up... So I really have not thought about this type of stuff for some time.

The other option is to plug the pump into a smart plug with power monitor. When power = 0 Watt, turn off ATO.

The fill is really random, open top so evaporation varies widely based on humidity / temp of the house.

the pump isn't powered directly, it's pretty tiny and it's powered through the same doohickey (logic circuit I suppose) that the sensor is powered by - (https://www.coralvue.com/smart-ato-micro-120p)

need to do something like this:

Ah! Maybe a relay setup then? Zooz has a few... If you put a float switch in the reservoir it could be used to trigger the switch input on a Zooz relay.

thanks this is kinda what I was thinking - though not sure what to use for the 2nd float sensor... I considered cannibalizing another ATO, but then it would be beeping :stuck_out_tongue:

Maybe I need to tear one apart and figure out the circuit that is doing the beeping could be used as an input for the relay?

I was hoping there might be sensor somewhere already - like there are water leak sensors, but the opposite - like a "no water" sensor :smiley:

Smart plug can detects down to a Watt and your pump/ATO spec is a round 4 Watts.

You can get a ZigBee plug for around $20 on Amazon. You can return it if it didn't work.


There are a slew of float switches out there that are just simple magnetic switches. Something like these:

If you turn it one way when mounting it floats when the water is higher than it opening the switch and closing it when the water goes below. Mount it the other way around and it will be closed when the water is high and open when it is low. Either way a relay (like the Zooz) could detect the open/close and shut off the ATO when the reservoir gets too low (but before the ATO starts being annoying) depending on where you mount it.

I used to use (I still have it but do not need it for the size tanks running) a water storage like the image below. It had 3 float switches. The red one at the bottom was the "too low" one and shut off the top off pump no matter what when it became closed, but turn on the RODI system. The green one in the middle was the "good" one and told it to restart the top off pump (if the tank was low itself). The top orange one was the "all full" (if closed) that left the top off pump running but shut off the RODI system.

Thanks but I’m not sure how I would be able to discern the difference of “the pump is not running because the power draw is less than X” due to the reservoir being empty and the device has paused itself- or just doesn’t have any work to do at the moment

Thank the reserve tank is glass so hopefully I find something like the optical sensor

Hmm... That does make it more difficult (although I have drilled tanks I found it pretty stressful). Maybe using a float switch hanger on the back? Then you can just use a vertical float switch (instead of the horizontal one I linked). Or you could use a magnetic holder.

Here's another weird idea by using a contact sensor. Mount the sensor outside the tank at the level you want to shutdown the buzzer. Put a small magnet in a little floater inside the tank and using a fishing line to set the magnet to the sensor level.
This should work unless you have a very thick glass.

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interesting - I get where you are going with this - so the magnet would float until the water ran out then gravity would take over and the line would make sure it met the sensor.

in leu of the fishing line I could actually see if there was some way to capture a floating magnet inside a small plastic "cage"

Most likely the unit uses a piezo speaker to produce the beeps. You could open the enclosure and put a piece of electrical tape across the top hole. That will lower the volume significantly and won't be heard unless you are near the tank.

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found this searching for "z-wave water level sensor" Zwave Pool Level Switch - YouTube

similar approach with a different hack for a sensor vs relay... similar concepts.

Thanks all for the suggestions - I'll post back when I've come up with something.

I'm guessing if I tried to use a water leak sensor and configured to only alert me if there wasnt a "leak" I'd wear the thing out in no time.

Couldn’t you jus have it cut the power to the pump when there is no water, and send you a notification? It would just send a dry event, when it’s dry, and a wet event when you fill it back up. Shouldn’t use up too much of the battery…

That's not a z-wave sensor. It's a Visonic ZigBee MCT-340E contact sensor.
I actually use a similar sensor MCT-310 for my pond to fill up the water with an Orbit zigbee garden Valve but you will need external power to the sensor because the battery doesn't last very long in "wet" state. Forgot all about this until this post :rofl:
I will see if I can snap a few pics of the sensor.

ah ha! - it looks like someone has built one!
Sea Side Aquatics Magnetic Float Switch

This is exactly what I envisioned!

I like the pill bottle/damper idea to prevent pump oscillations.

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