Thanks Jonny,
I don't know how all of you guys top off your water but being I started this thread I will get into it a little the way I do it.
I guess you figured out that I like to build and modify things. My top off system is totally automatic and I only have to touch it every year or so.
I hung this (blue) bucket from the ceiling in my workshop so it is higher than my reef. The water flows to the RO unit through an electric valve. As long as the valve is energized, water flows. From the RO unit below the bucket, it flows to the acrylic DI to the left of the bucket. From there it enters the bucket. As the bucket fills, it raises the float which is a film container connected to that pink string. The string is connected to an old thermostat mercury switch so that when the water rises, the float rises lifting the mercury switch which shuts off power to the electric valve and the water to the RO stops. The bucket stays filled.
There is also a tube coming out near the top of the bucket in case this arrangement fails and the overflow would go down a drain, but that has never happened.
There is a PVC hose running from the bottom of the bucket, over my ceiling about 25' to another acrylic container on the tank with more DI resins and from there to a float switch on the tank.
This arrangement is designed to only supply water to the tank at about a drop every 3 seconds. The tank normally only needs a drop every five seconds so in the event the float switch gets stuck (which also has never happened) it would take a few days before the tank would overflow and it would only overflow a few drops an hour.
Under the tank is a DIY overflow safety switch which consists of a wire from a GFCI receptacle. The pumps on the tank are plugged into that GFCI so if there is a leak, the GFCI would trip off, shutting down the pumps.
I am sure everyone on here uses the same system.
Float switch