How to Start a Reef Tank: Test Kits

Water testing is an essential part of any successful reef tank maintenance program. We call ourselves ‘reef keepers’, but ‘water keepers’ is actually more accurate. We’re constantly testing our water for detectable phosphates, checking that the alkalinity is balanced and stable, and looking for changes in calcium levels. All of this attention to our water ensures that our corals have the best possible conditions to thrive and grow. Since these parameters can have a dramatic effect on the health of our corals, we need to have the proper test kits on hand.


Long term, alkalinity and phosphate are probably going to be the two you test for most often. Other than alkalinity, most parameter results are read in Parts per Million or PPM. Here’s a quick run down of what test kits are commonly used on our reef tanks and why we need them:

    • Nitrate (N03): The result of the nitrogen cycle from fish waste and uneaten food. Beneficial bacteria convert Ammonia into Nitrite and then Nitrate. Nitrates feed algae, so we try to keep these as close to zero as possible by not overfeeding and with regular water changes.
    • Phosphate (P04): Phosphates, much like nitrates, can come from fish food, additives, decaying matter, etc. It can also be present in our tap water. Phosphate can inhibit coral growth and feeds algae. Water changes and careful maintenance will keep it low. The REEFED office tank sits at around 0.01-0.05 ppm.
    • Alkalinity (dKH): Measured in degrees of Carbonate Hardness (the K is from the German “Karbonathärte”). Used by corals to build their skeletons. Many corals are very sensitive to fluctuations in alkalinity. Keep this stable. Typically between 8 dKH – 10 dKH is a good goal.
    • Calcium (Ca): Also used by corals to build their skeletons. Should be kept between 380 – 480 ppm in most systems. This is less critical than alkalinity.
    • Magnesium (Mg or Mag): Simply put, corals struggle to process the available calcium and ‘alkalinity’ without proper magnesium levels. Magnesium depletes much slower than calcium and alkalinity. A tank requiring 40 ml of the other two dosed daily might only require 2-3 ml of magnesium.