About Tetenal Protectan, from Jobo site:

" A fourth way to extend the life of the solution is to use a non-oxidizing gas to replace the air in the bottle. Tetenal manufactures an aerosol (no CFC's) gas which can be sprayed into the mouth of the bottle to displace the air. As with all aerosol type products, avoid sparks, flames or smoking while using the products, because virtually all aerosol propellants are flammable."

So, a gas lighter refill bottle (butane) is way cheaper...

Jorge O