RO and RO/DI systems remove impurities—chlorine, chloramines, pesticides, phosphates, heavy metals and many others—from tap water. These impurities may contribute to the growth of nuisance algae, while others can cause even larger problems.

DI (De-Ionizing) cartridges do an excellent job of removing phosphates, silicates and nitrates from tap water. They are highly recommended for reef tanks but work just as well for fish-only tanks.

There are a ton of installation accessories available for RO and RO/DI units, probably the most useful being a drinking water kit.

Other tap water filtration systems are available, too, such as the Poly Bio Marine Kold Set-il Filter System.