FOWLR and FO with any rock/sand is the same thing.
You don't need RO unless you are doing coral. Even then you don't NEED RO, it just makes it easier. Reverse Osmosis is just a VERY fine filter to pull particulate out of the water.
You don't need RO unless you are doing coral. Even then you don't NEED RO, it just makes it easier. Reverse Osmosis is just a VERY fine filter to pull particulate out of the water.