Originally Posted by kdpuffer
Agreed, if you can eliminate the head height aqua lifter is best option. They can safely run dry.
The JBJ ATO run in mode A uses one of the floats as a safety in the top off reservoir to keep the transfer pump from funning dry. In mode B, the higher float as I understand the instructions is actually the "off" switch. The unit will still turn on the pump even if the lower float valve is floating. (Both float valves have to be up to turn the unit off.)
The dual float ATO controller from autotopoff.com uses the higher float valve as a fail safe to turn off the unit, even if the lower valve is stuck in a lower position. (If either float valve is up, it turns the pump off.)
The JBJ's fail safe is an electronic timer which will only let the pump run for 3 to 7 minutes at a time before resetting itself. I used a JBJ with an Aqualifter on my 75, and because of the timer and the evaporation rate, it couldn't keep up. I ended up switching to a MJ600 and haven't had any problems, but could have once IF my ATO reservoir was significantly larger when the sump float valve got stuck due to calcium deposits. (The reservoir I use is only 3.5 gallons.). The JBJ fail safe can protect the transfer pump, but doesn't do much to protect from dumping too much freshwater back into the tank should a float valve get stuck. The autotopoff.com design is safer for the tank.
IIRC, the Tunze Osmolater uses a mechanical float switch and an electric eye as a fail safe to prevent an overfill. I believe it also includes the transfer pump. Since the electric eye can't get stuck like a float valve can, it's considered to be pretty reliable as well.
Hydor just came out with an ATO controller that is very compact and uses the difference in temperature between finger-like probes to turn the pump on and off you might consider as well. I guess it's a different technology than what else is out there, and may have some bugs we don't know about yet though.