I have/use the Hydor ATO. I use it for my sump when water level gets low. It may be slightly more complicated for you if you desire to have a water container next to your tank (which doesn't have a sump) since you would either 1. Need a pump strong enough to push the water from the ground up to the top of your tank. 2. Elevate the water container on a table next to the tank, then you can get away with a weaker pump.
I have my pump in a 5 gallon bucket and drilled a hole on the lid so that the tubing can come out from the top of the bucket. That way the bucket can be sealed and your RO
water won't get contaminated by dust, other animals, or mischievous children. It has worked very well, so far. I have only 1 complaint which I have found a nice work around for. It’s LOUD!
It depends on where you have your tank (Bedroom, living room, garage) and when the pump decides to turn on. But for the most part, my ATO fills it to the max line and it alarms. It will continue to alarm until you either 1) turn it off and remember to turn it back on. 2) Let the water naturally evaporate until it’s below the max line and then the alarm automatically turns off. I never went with option #2. My water line stayed at the max line for at least 12 hours. No way was I going to listen to that alarm for that long. Option #1 is risky if you forget to turn it back on, but also defeats the purpose of having an ATO all together. So I opted for my “Option #3”. Buy a timer and have the ATO turn on for only 10 minutes at the same time every day. This will ensure that your tank never runs dry and you will only need to listen to that noisy alarm for about 7 min, it takes a few min for it to boot up.
So basically, since getting the timer, this ATO was worked very well for me. Just know your rate of evaporation. My 5 gallon bucket of RO
will last about 7 or 8 days. So plan carefully if going on vacation or being away from home. Hope this helps.