Very Best Switch or Sensor for ATO System?

[herring_fish]

I'm looking for the best switch for an Auto Top Off system. My first step is to find out what would be the very best TYPE of switch that I can afford. Then I can zero in on the best model of that type.

Background:

After 25 plus years of reefing, I had a total tank crash of a 120 gallon tank while on vacation. I set a homemade ATO system wrong so it overflowed from the second day until it was discovered by my tank sitter and that was too late. That was all my fault but now I am uptight about choosing my next system.

I am now rebuilding with a bottom up system with a new 180. I have more money for the re-build so I am going with more high end products.
I read lots of stuff including a few pretty good review articles and different systems had advantages like software, pump, solenoid etc. but I want to concentrate on just this component by itself for now.

I think that I will buy an Apex system but I already have the plumbing, solenoid and many types of peristaltic pumps.

Back to the point:

Since I lost a tank because of an ATO system, I want a switch that is really reliable, low maintenance and perhaps accurate. These things are normally very cheap compared to some of the other parts of the system. That is why I want to buy whatever is the best. Of course I don't want to buy some kind of atomic refractory laboratory system for thousands of dollars but I don't mind paying a few more Benjamin's if needed.

I know that many people will say that a simple float switch is all that I need but I had a mechanical one and got water on the floor several times, for different reasons, before I got rid of it. I went to electric float switches. To feel safe, every month or so I had to move them up and down several times to make sure that they didn't stick. Personally, I want something that I don't have to check, clean or un-stick every two weeks or months.

There are lots of choices. Some are standard and used by other ATO systems and others are a little more off the wall. Some of the choices are:

Float (sticks)
Conductance (corrodes)
Vertical Pressure (fouls)
Capacitance (corrodes)
Optical or Ultrasonic sensor (would salt creep coat it?)
Horizontal Pressure (new would it corrode?) https://www.youtube.com/watch?v=_q2TIU_PfYg
A salt water tank is subject to many things that make me deal with thinks that are dirty, sticky, viscous, corrosive, and crystallizing.

What do you think would be the best ATO switch or sensor that is available out there for me?

 

[kenith]

I'm not sure what controller you're using, but try an apex with a breakout box and redundant switches and program to turn off the pump in case. I use one switch for standard on/off, another that sits 1/2" higher than the first that cuts the pump off if that sensor is triggered, followed lastly by programming the apex to shut the pump off if it runs longer than xx seconds/minutes. Failsafe

Edit: I use float switches. The higher switch that does not touch the water doesn't have salt buildup or anything growing/crawling on it.

 

[DaveMorris]

Check out the digital version of the Avast Marine top off kit. I use this setup and absolutely love it. It works using a rigid 1/2" tube that is mounted vertically and an air line runs from it to a small box that houses a relay that is driven by air pressure. As the water level goes up and down inside the rigid tube it will trigger the relay. It works great and has no moving parts to fail. If you do get an Apex you can get this top off sensor pre-wired to connect directly to the Apex as a trigger switch to turn on your top off pump. It is easy and foolproof.

 

[herring_fish]

Product:
https://www.sparkfun.com/products/10221

Specs:
http://cdn.sparkfun.com/datasheets/Sensors/ForceFlex/eTape%20Datasheet%2012110215TC-8_040213.pdf

A youtube file:
https://www.youtube.com/watch?v=c3VJPi1TeSY

I found this a few days ago and have been researching it ever since. It’s a variable resister that is totally sealed below the water line and can take falling totally under water, short term. I believe that it works on pressure. The spec.s say that it is not for corrosive use but they are talking about harsh acids and the like, not salt water. According to a tech. that answered questions on a thread, it is not susceptible to salt creep and it just looks cool to me.

On the down side, you have to put together some electronics to hook it up. One user said that his friend had some issue with accuracy. I think that he used the simple code and didn’t use the mapping function to do a fine calibration on an Arduino. The unit is supposed to be good down to .010” or .25mm.

It would be nice to be able to actually plot the water level with a graph on the Apex, instead of just having a binary On or Off with a second sensor backup to perform an All Stop if the first one fails. Of course I would use a different type of sensor for my back up.

I’m not looking at this unit completely because of logic. Part of it is emotional. On the other hand I don’t want to bet on a loser so I will keep doing research.

Does anyone have any feedback on actual use of this sensor?

 

[acrohead500ppm]

I know the new spectrapure ATO is supposed to be great, BUT only thing I can personally endorse is the tunze osmolator.

 

[ca1ore]

Any kind of mechanical device will fail, it's just a matter of time. The key, in my experience, is to run these devices redundantly, either two or even three. That way, should one decide to fail, the second is there to act as a backup. If you are going to buy an apex, then I agree with the prior post that you should use a breakout box to easily manage the multiple sensors. Personally, I use the avast pressure sensor connected to my apex as the primary switch, but two additional Madison floats as backup.