Saw an ad on fb marketplace for a used reverse osmosis system that was used for a saltwater aquarium for 50 bucks . Itís called a typhoon . I already spoke to the company in Florida that manufactures them and am asking for anyone here if you have one that has the fourth filter what you use it for. The manufacturer or distributor say the fourth filter removes all minerals from the water this device has to be of some use after shtf possibly for aquaponics. Any takers?