[untamed]

Originally Posted by Fish

....And the tank is never left long enough without a water change to make a difference. I used one of these pumps to dose a 2gal nano for a couple years and it would take at least two weeks for the water level to creep less than one centimeter either up or down. Because I was usually doing water changes more often than that, it was never anything I had to address....

I've gone both ways and the float switch worked way better for me. I'll offer two ideas that could give you peace of mind.

1) Use two float switches for redundancy. The chances of both switches failing at the same time is pretty remote.
2) Push the water in through VERY low volume irrigation drippers. That way, the system is incapable of delivering water really fast, even if the floats fail. If the float got stuck "on", it would still take 24 hours or more of continuous pumping before the tank level would start to rise.

One question though...When you do a water change, it is only a partial volume change, right? You're not doing a 100% water change. So if your evaporative system has pumped a bit too much water in there, you will have diluted the system and will be running slightly low salinity. If you want to correct this during a water change, you'll have to adjust the salinity of your replacement SW higher to compensate.