Kalkwasser is the oldest method of calcium dosing for reef aquariums; first pioneered by German hobbyists decades ago. Calcium is the key to healthy corals and other invertebrates; and kalkwasser is a popular way to do so. Kalkwasser is a powder that must be mixed with the appropriate amount of water and then this solution must be added very slowly; through some sort of dosing mechanism; to the aquarium. Kalkwasser solution has a very high pH; and will alter the pH of your aquarium. This is beneficial when done gradually; but raising pH too quickly with kalkwasser will pretty much guarantee destruction. Kalkwasser is best for lightly to medium stocked tanks; rather than tanks with a high load of livestock. Kalkwasser may not be able to keep calcium at high enough levels to benefit a larger number of corals. This is why many aquarists use another calcium product in addition to their kalkwasser dosing. Kalkwasser definitely has its benefits for the right tank. It not only allows aquarists to slowly dose calcium; it also helps precipitate phosphates; which can lead to excessive algae growth; among other problems. Because kalkwasser helps boost pH; it is good for tanks with chronic low-pH problems; as well. Phosphate and nitrate free. Treats up to 27;000 gallons of water.