Please see the image before reading on!!!!
In my 12 gallon long, I estimate I lose about 500 mL of water per day through evaporation.
My peristaltic pumps average approximately 100 mL or water per minute.
Therefore, I use a timer to turn the pump on for 3 minutes per day (600mL of water per day)
Any excess water gets pumped back into the reservoir as the water level reaches the inlet of the output tube (output from tank back into reservoir)
If that level is not reached, the pump will simply push air back into the reservoir instead, to replace the water that is pumped into the tank.
Peristaltic pumps are rated for both air and liquids, so there is no risk of burning out or causing a fire.
There is also no risk of overflow since any time the water hits the maximim level, it is pumped right back into the reservoir
You can adjust the desired water level by adjusting the heigh of the output's inlet tube
You can adjust the amount of water being pumped in per day by adjusting the length of time the pumps are turned on per day. eventually, your ATO will harmonize with the average water loss per day as you adjust accordingly. Just to be safe, always pump in a little more than your estimated loss.
Just note: this is really only useful for small tanks. Anything larger, will require a larger pump, and these peristaltic pumps can get quite expensive as they increase in size.
Mine were 20 dollars each from Amazon