OMG! ATO got stuck on!!! Almost had a flood!!

Big problems ensue having a straight RODI to tank setup. Either get a reservoir for the ATO, or do manual topoffs.

Let's put it this way. My tank has a 5.5g reservoir for the ATO. The sump can hold the full ATO, plus the overflow if there's a power outage for the return pump. It's a BlueLine Tsunami AT-1, which has no electronic or mechanical parts inside the tank. That makes it inherently more reliable than the majority of other ATO systems. (If you're wondering, the unit works with a piece of airline tubing, which leads out to a pressure switch. Whether it's on or off is based on the pressure in the tube, which changes based on the water level.)

Then, it's on a RKL, with a 3 minute timer per day, divided into 3 separate one minute intervals. The pump is about 50 GPH, so it can only ever pump a gallon on the timer. It's not hooked up to the RO, I add water to the ATO tank manually. The RKL will also prevent the ATO pump from burning out if the water level gets too low in the reservoir.

See how super redundant that is in terms of safety? In the absolute worst case scenario, my tank gets a slight salinity drop (5G dumped into to 65G water volume, mixed slowly up to the DT via the return pump isn't huge), and never overflows, but even then it would take so many things going wrong it's absurd. That's the type of thinking that should go into an ATO set up (also for overflows IMO), where the absolute worst case scenario isn't really all that bad.

 

ATOs should be taken very seriously, they definitely will fail and if your in the hobby for a long time, more than once.

I have a few layers of defense at the moment.
1) I only keep a 5g bucket. This has to be filled about every 3 days, but does not allow any significant change in s.g. My systems total water volume is about 140g and I keep the s.g at 1.026. So, even dumping the entire bucket in would only change it to
about 1.025.

2) ATO controller has a low water "on/off" switch and a high water "off" switch.

3) A dose kalk, so I use an aqualift pump, with a flow restriction valve set to about 2-3 drops per second. I've calculated about 20 drops per ml, so, this works out to about 75700 drops per gallon. So, this is only about .14g per hour, and over 24 hours, only about 3.4g. I get 1.5 gallons of evaporation per day, to the net difference is about 1.92.
Therefore even if the ATO malfunctions for 24 hours, I'd actually only drop the s.g. down to about 1.0254.

4) As I said it's on a kalk drip. So, I decided to also have the ATO plugged into a controller. If the pH rises too much, it shuts off the ATO. I've been playing with this, but currently have it set to pH 8.3.

I have a system this complex because after roughly 10 years, I know St Murphy very, very well

 

I had a friend that went on vacation for two weeks. RO under the kitchen sink popped off. Flooded house. 30,000 gallons they had to pay for that month. They lived in a motel for 6 weeks while their house was gutted and rebuilt. Lost everything downstairs.

Not fish related.... but moral of the story.... do not take plastic lines hooked up to water mains for granted. RO/DIs are serious business.