Liter Meter 3 with back up float valve module. 15 years plus, ZERO failure. Because it's a peristaltic pump, it can never back siphone. Because it uses air pressure switch as a back up, it can never stay in "stuck" like a mechanical float valve. Because you can program the amount in volume it can dose in 24hrs, it will never overdose. Because you can calibrate it once its in position, it is extremely precise. It IS pricey but you make your money back the first time it saves your tank. Because the parts are durable and the unit is easily serviced, it can last almost a lifetime. I have a friend who still uses the original Liter Meter I, still going strong after 15 plus years as well.