When maintaining an aquarium with corals, it is crucial to uphold specific levels of magnesium, calcium, and alkalinity. Without testing for these elements, your success with corals may be short lived.
Most importantly, buy an accurate test kit. The few extra dollars spent on a reliable test kit can save your corals in the case of any swings.
You should be testing your water about three times a week in order to keep the levels stable. A more stable tank provides a healthy environment for your corals to grow in.
When beginning a tank, you will not have that many corals; therefore, when you do water changes, the calcium, alkalinity, and magnesium will be replenished in the new salt water. Once your corals begin to grow, their needs of the elements will surpass the amount in the salt and you will have to dose them. Each aquarium will need a different amount of magnesium, calcium, and alkalinity.
First, test your water. Then, add less of the deficient element than you think you need. After half an hour, test the water again. Repeat until the desired level is reached.
Record how much of the element you added all together so you can figure out how much solution it takes to raise it a point(s). Once you know how much to add and how often you need to dose your tank, you can set a dosing pump to dose for you.
You will still need to test your water when using a dosing pump. As your corals grow, they will consume more of the elements.
Some people prefer maintaining the necessary elements with a calcium reactor but both methods require regular testing. These elements provide the materials needed for corals to grow and without them their health will surely suffer.