Righty: MAN o MAN!! I should have started my own website.
I have been using float sensores like that ( on ATO.com) since around 96'. ( ?) I used to get them from American chemicals CHEAP CHEAP ( .40 )because my aunt was the pesidents personal assistant.
I got alot of crap at what it cost them to make it or actual bulk price per unit they paid! LOL!!
Manny: yup. BUT search ebay for ones from the US. Shiping is like $6 bucks EACH on those from china.
I will see if I can get some from a friend that lives in Hong kong.
I'll post when I know.
On my old system i used the Ultra Life Float Switch it failed due to caretaker error dumping 40 gallons of RO/DI into the tank, it never worked correctly after that.
I now use the Reef Fanatic Level Controller, had zero problems with it in 2 years, having 2 switches, one switch as the top off sensor, the other as an emergency shut-off should the first stick on.
See page one for my set up, but I am using all parts from auto top off except the pump. Look at the DIY plan link to see where the pump fits in. The water is feed to the system via gravity feed, the pump, an Iwaki 10, is used to fill the upper container and it on a timmer to run for 5 minutes a day, refilling the upper container. I have been running this since Christmas time and it is amazing. I wonder what I did with out it for so long. Oh I remember slept buckets and had fluctuating SG
Its a snap to hook up. Only two wires.
All you do it wire it in series with an extension cord on the "fat" side.
DO NOT USE ANYTHING LARGER THAN A MAXI-JET 1200.
That will be more than enough to pump fresh water through a 1/2" section of tubing feet. ( thats what I do )
I use a ten gallon tank and a maxi-jet 1200.