Over time your system will start to accumulate phosphates and nitrates. There are pretty much three accepted methods folks use to remove them.
- Water Changes (20% or more) as often as you can.
- Bio Pellet Reactor and/or Granulated Ferrous Oxide (GFO) Reactor
- Refugium full of Marine Plants to consume the phosphates and nitrates.
The acceptable levels for these substances are Nitrates at 4ppm and Phosphates at 0.03-0.06ppm. Less than these amounts and some of your corals will fail as they need them for food.