Reverse osmosis water filtration systems may seem complex, with multiple stages and various filter types to account for. The dizzying number of options available to the casual hobbyist usually frustrates potential users, who end up settling for simpler setups that lack the filtering abilities needed for a full blown reef aquarium. Many hobbyists can get by with simple, but in an age where municipalities are constantly adding things to their water, such as chloramine, the standard systems are no longer enough and the detrimental chemicals sneak by. Because of this, I’ve always suggested that when it comes to RO units, go bit of go home. Yes, the large number of stages and the different filter types can be daunting, but most manufacturers assemble these stages properly all for you. And when it comes time to replace these filters, just mimic what the manufacturer did, unless of course you realize deficiencies in your system and choose to go your own route.