Dosing a Saltwater Aquarium

Dosing a saltwater aquarium is important to keep the tank’s parameters as close to real ocean parameters as possible. Doing this will give you the best results and a very healthy tank. We have been dosing KH over the last few weeks, since our KH tests were coming out at 7 dKH, with the recommended range of about 8-11 dKH, depending on who you talk to or where you get your information. We decided to shoot for a 9 dKH, which seems a safe number no matter the recommended range. The product we use is by Seachem and is slowly helping to increase our KH levels.

Dosing a Saltwater Aquarium

There is so much science, equations, and in depth explanation to reef chemistry, but we will just stick with the very basics.

KH (Carbonate Hardness) is also known as alkalinity, but not the pH measurement “alkaline”. It does affect pH, but it is not the measurement of pH. KH measures the concentration of hydrogen carbonate, as well as carbonate ions in water. The concentration of these ions gives a good idea of the capability of water to maintain proper pH levels, because the carbonate hardness acts as a buffer against fluctuating pH levels. If KH is too low, the pH value of our water may drop to a more acidic level and be life threatening to our fish and invertebrates.

But why do pH levels fluctuate? The pH level of our tank during the day can be quite a bit different than late at night, after the lights have gone out. This is because during the day the photosynthesis process causes the CO2 levels in the tank to decrease because of the corals and algae absorbing it, which results in a more alkaline pH. And then at night these corals and algae release the CO2, causing a more acidic pH. CO2 is a by-product of the metabolic functions, or respirations, of the tank. CO2 affects not only the pH, but other levels as well, such as calcium. Aside from dosing, keeping a light on the refugium opposite of the tank’s light cycle helps to keep a more constant CO2 and pH level. We have added a light in our refugium already, as well as Chaeto, which is an algae. Also, high amounts of circulation and aeration help remove CO2 from the water, as well as allowing some algae growth to consume the CO2, and of course, not overfeed or overstocking.

We purchased the Reef Fusion two part system, the 2nd part being the calcium dose, because currently our calcium levels are fine, but corals and coraline algae need adequate levels of KH and Calcium to build their skeletons. At some point, we will need to dose both, and that’s why we purchased the product that we did. The calcium dose of this two-part product is 4mg/L and 0.176 meq/L of alkalinity at a 1:1 ratio. This information will be helpful down the road when we are dosing both, to calculate how much our calcium and alkalinity levels should be rising.

Corals and coraline algae are not the only life in our aquarium that requires calcium. Snails and other invertebrates will use calcium for their shells. The rough range for calcium is 350-450 ppm (parts per million). I find that this range also  varies slightly depending on source. Our Calcium level has been around 380 ppm. Once it falls below 350, we will begin dosing.

Since we have been dosing KH we have had an explosion of coraline growing on our rocks and especially the back wall of the tank as seen below.

Dosing a Saltwater Aquarium

This coraline algae is a sign that we are hitting the mark on our KH. Also, our corals have noticeably grown, especially our pocillopora coral, which has almost doubled in size!

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