Marine

A marine aquarium needs more planning than a freshwater one, because corals react to even small changes. Before you start, work out where your clean reverse osmosis water will come from, how you will mix salt water for water changes and how you will measure salinity. Dry reef rock needs several weeks to be colonised by bacteria before livestock goes in.

Stony corals use calcium, carbonates and magnesium all the time. That loss is covered with Balling solutions or ready-made additives, but the dose comes from testing: start low and increase it only when the test shows the level falling.

A common mistake is changing several things at once or chasing perfect numbers. A value that holds steady for weeks is better for corals than a quick correction. Add coral foods and trace elements once the main parameters are stable.