It seems to have many electronic components. The only concern I would have is the failure of one. If it is the wrong one at least your sleep will be uninterrupted as it overflows onto the floor. But, you will be all rested in the morning to deal with it.
But seriously, I have contemplated a system that is automatic.
My thought was have water flow in continually (Either declorinated before entering, or wait until I drill my water well).
As the water flows in slowly through a needle valve, the water will flow out through an overflow.
No moving parts. The main issue we be to be sure to keep the overflow and overflow line clean.
I looked into filters that can remove chlorine to put inline. But you have R.O.

 

You're right about the components. I am using a lot to accomplish this. I too am afraid it might leak but I've got both mechanical and electrical components to help stop this from happening. The first line of defense is the inferred eyes that measure where the water height is at. When the top one is triggered the water solenoid is cut off. If it fails to read there is a float valve preventing the water from getting any higher. If the float valve fails I'm placing a leak detection monitor on the floor and in the tank stand. If either sensor detects a leak an alarm goes off, the solenoid feeding the ATO shuts off, and an alert is sent to my phone via push notification. It should be enough... I hope.

I've seen the continual flow thing done a few times. I like the idea but since I'm not running a sump I'd have to drill a hole near the top of the tank to outflow and cutting a hole near the edge of the glass is risky and of course, there is the issue of clogging and leaking which you'd still need at least a float valve and/or electronic solenoid to keep the system from overflowing.

 

Automatic water changes are a thing that has been done a LOT. The way you want to do it, is definitely not the way unfortunately.

Solenoids fail and sensors fail. Frankly in this system your weak link is the sensors. ATO and automatic water changes are not as common in freshwater, so if you want to see some disaster stories you should head over to a saltwater forum. They are extremely common over there because most people have an ATO and those ATOs fails eventually.

BUT there is an easy solution to this problem. You simply drill your tank at the maximum height of the water level, and let any water drain out from what is usually an open and dry drain. You can have a refill solenoid if you want, or you can do a a very slow drip refill that runs constantly throughout the day. This last is how aquarium co-op runs all their store tanks.

It also avoids the failure problems associated with sensors. Instead if the solenoid (if you choose to go that way) fails to open, you simply won't get a water change that day, and you will figure out what happened when you notice your water level lower then normal due to evaporation. If it opens and stays open, you will hear the water going down constantly through the dry drain. An oversized 3/4 or 1" bulkhead will be big enough to ensure you don't have problems with a clog. Good luck!

 

Automatic water changes are a thing that has been done a LOT. The way you want to do it, is definitely not the way unfortunately.

Solenoids fail and sensors fail. Frankly in this system your weak link is the sensors. ATO and automatic water changes are not as common in freshwater, so if you want to see some disaster stories you should head over to a saltwater forum. They are extremely common over there because most people have an ATO and those ATOs fails eventually.

BUT there is an easy solution to this problem. You simply drill your tank at the maximum height of the water level, and let any water drain out from what is usually an open and dry drain. You can have a refill solenoid if you want, or you can do a a very slow drip refill that runs constantly throughout the day. This last is how aquarium co-op runs all their store tanks.

It also avoids the failure problems associated with sensors. Instead if the solenoid (if you choose to go that way) fails to open, you simply won't get a water change that day, and you will figure out what happened when you notice your water level lower then normal due to evaporation. If it opens and stays open, you will hear the water going down constantly through the dry drain. An oversized 3/4 or 1" bulkhead will be big enough to ensure you don't have problems with a clog. Good luck!

Ok feedback received thank you. However, if my weak link is the sensors and I have a mechanical backup (float valve) doesn't my redundancy count for something? Both would have to fail before the water hits the floor, and if it does I'm alerted the moment the leak detectors sense water. I used to be in the saltwater hobby for 10 years before getting back into the planted tank side of things. I ran a 230-gallon reef tank and I know the dangers of ATO failures first hand (never did AWC though). My Apex leak detectors saved me a few times already, but I didn't have any redundancies as I have shown here.

You're giving me some food for thought though. I could add 2 additional IR sensors or perhaps even electric float switches (which would depend on a different Apex module) in conjunction with the IR sensors that would alert me if the initial one failed. Example: IR Sensor #1 fails, a float sensor above it triggers, RO solenoid turns off, alerts sounds on the Apex, and sends my phone a push notification of the failure. With that at least I'd know if the system was depending on the float valve and something was wrong with the sensor or solenoid. If the mechanical float valve does fail too, the floor gets wet, triggers the leak detectors, and hits me with a notification. I could do the same thing for the lower AWC sensor too, that way I'd know if it fails.

Drilling glass near its edge (the top of the tank) is a risky procedure. I've seen that go wrong as well. A 3/4 or 1" bulkhead below my tanks rim of would leave my waterline nearly 2 inches below the top. Not an attractive look IMO. I like your idea for its safety though.

 

I like the metered flow in with an overflow. So simple. So cheap. So reliable.

 

AWC is a very common thing in reefing. I have been meaning to set it up on my large reef tank I have just been slacking on it.

if you have the Apex why not get the DOS and do smaller WC daily that is what most reefers do. I plan on doing around 1.5 gal. per day on a 160 gal system. doing smaller Wc will keep the tank supper stable while still exporting the wast.
most reefer do around 1-2% daily WC i dont know what % would work best for FW tho. guess it all depens on your filtration and stocking level.

just a thought.

yesterday I got my WC set up for my soon to be 1st aquascape I got the phyothon and a sicce pump but after all that I thought I should have just done AWC. IDK maybe down the rd. I can drill more holes in the floor to the basement. ha

 

I have view of this you may or may not like, but here goes. Like you i have been down the saltwater tank road (15yrs) and had an auto top off. I Also have an Apex from the pervious salt hobby. I currently have a 245 gal display with 180 gal sump( also reef leftover). In my setup i use the Apex to monitor parameters and control c02 and shutting off my return for feed mode. I have a separate Tunze ato that pulls from two 55 gal drums tied together that are fed by a by-passed RO filter controlled by a manual float. In my case water changes are 110gals each and i am equipped to do two back to back in case of emergency. I do believe in some automation, but hands on gives the opportunity to see things that are happening like float valves that don’t shut off all the way before they become a 3 am flood or worse. Another thought is i want to remove a volume of water completely and dilute the rest. If you really want to go continuous do a acrylic sump and drill it where you need to. I wish you dry floors and clear water.

 

I suppose I could do a small daily AWC, though I don't think I need the DOS though since I've already got a pressurized RO feed to the aquarium. Smaller daily AWC's would be less shocking to the overall system.

To the point of drilling out the tank and installing a bulkhead, I can really see its advantages and safety and am considering it. It does add to my build though. I'd have to not only drill out the tank but run a drain line from the tank to the sewer. Initially, I was just going to drill a small hole in my wall and pipe the water to a garden just outside. We get cold winters here in Northern Utah and I wasn't so much worried about a 1/4 or 3/8 drain line that would generally be empty but drizzling out water continuously might ice over. I'm still thinking it through though. I may try my method and leave myself the ability to add a drain line if it does become problematic.

As for running a sump and doing ATO or even AWC through the method, I have to take a hard pass. One of the only ways I could convince the wife to allow me to do this was in our front room was a promise that it would be silent. I've never met a sump that wasn't in some way noisy. Either it's the splashing of falling water or is the hum of the pump. Just quiet is not good enough. It's got to be silent.

 

I would use a small pump on a timer and a float valve for make up. The pump would be high enough not to drain tank and will only need to run for short time. siphon should break itself. RO is slow so will not over take the pump. Could drill drain overflow just in case this could be used to prevent siphon as well by running pump drain line to it ( smaller line looped inside above waterline).
There is the issue off keeping the filter running but this depends on how the overflow box is setup.

 

As everyone has stated, there are many ways to do this. In my breeding and grow out rack i use a simple drip method with an irrigation valve and timer. The water runs through carbon blocks and using drip emitters meters the water to the tanks on the days, times and amounts i choose. The tanks are drilled for overflow that goes to a sump and gets pumped to waste. I generally do no more than a 10% change (it's really a dilution) per day, for this reason i've never heated the incoming water, the temp moves at most 1 degree for a very short time until the heater catches up.

For a simple actual water change, DIYforFun has the right idea except i would make a change to the filling portion. Drill the tank for a simple over flow (single bulkhead and just use a street 90 fitting to set water level) and using a reservoir of water, set a timer (use easy to set wifi timers for both pumps, like Kasa, etc.) to run a pump at a duration that fills the tank completely and just over flows slightly with the excess going to a drain, assuming you have access to that. Just make sure the fill line has a siphon break or that the outlet is above the final water level.

 

Wifi

As everyone has stated, there are many ways to do this. In my breeding and grow out rack i use a simple drip method with an irrigation valve and timer. The water runs through carbon blocks and using drip emitters meters the water to the tanks on the days, times and amounts i choose. The tanks are drilled for overflow that goes to a sump and gets pumped to waste. I generally do no more than a 10% change (it's really a dilution) per day, for this reason i've never heated the incoming water, the temp moves at most 1 degree for a very short time until the heater catches up.

For a simple actual water change, DIYforFun has the right idea except i would make a change to the filling portion. Drill the tank for a simple over flow (single bulkhead and just use a street 90 fitting to set water level) and using a reservoir of water, set a timer (use easy to set wifi timers for both pumps, like Kasa, etc.) to run a pump at a duration that fills the tank completely and just over flows slightly with the excess going to a drain, assuming you have access to that. Just make sure the fill line has a siphon break or that the outlet is above the final water level.

Wifi timers are awesome. But I still like to manually change water. I use a turkey baster and siphon to clean in between hardscape and clean moss. This cannot be down automatically. I also inspect and trim plants

 

Well after some issues I was having trying to remove some scratches out of my 90-gallon w/ overflow I decided to just buy a new tank. My stand was built around the Aqueon with overflow but after calling every LFS within 100 miles of me apparently due to supply issues this tank won't be available for some time. The only one I could find available was the Aqueon 90 without the overflow so I bought it. This kind of messes with my whole ATO/AWC so as they say I'm back to the drawing board.

At this point, since I'll definitely be drilling holes in the back of the tank I'm most tempted to do the previously suggested method of continuously dripping the water into the tank and allowing it to drain out freely. I'm thinking about drilling 4 holes. One in each corner for the filtration returns, one larger one in the center about 1/4 the way down the tank for filtration drain (I was considering using one of these low profile overflow strainers), then one close to the top for the continuous water change outflow that will be connected to my plumbing. I still plan on using at least one of my IR sensors and leak detectors in case water either goes above the determined waterline or a leak is detected. At that point, the Apex will close the RO feed solenoid. Regardless though this drip/drain method does appear to be the most foolproof solution.

With that, I'm getting prepared to run my drain and fresh water line to the tank. One question though: I plan to ATO with RO water. My tap water here is quite hard but I could run two separate lines and alternate between the RO and tap as often as I'd like. Do you guys think that would be worth it or just stick with RO and dose back whatever I need to replenish the lost minerals?

To give you an idea of my hardness my tap specs out:
tds 350
ph 8.2
dkh 14
gh 19

Also here is a pic of where I plotted out initially where I would drill the holes. let me know what ya think.