Have you ever asked yourself, “Why is my tank’s alkalinity rising?” It’s a question that frequently arises among reef aquarium enthusiasts, and for good reason – alkalinity plays a crucial role in maintaining the health of your tank. But did you know that there are many ways in which alkalinity can accumulate in a reef tank? Some of them may surprise you.
What is Alkalinity and Why is it Important?
Alkalinity refers to the capacity of water to neutralize acids. In the context of a reef tank, an alkalinity range of 7-12 dKH (degrees of potassium hydroxide) is generally accepted as optimal. Maintaining alkalinity within this range is important for several reasons. First, low alkalinity can halt the calcification process (i.e. growth) in organisms containing calcium carbonate, and can also stress corals by reducing the amount of carbonate and bicarbonate in the water. Low alkalinity can also suppress pH, which can dissolve coral skeletons if the pH falls below about 7.5. On the other hand, very high alkalinity can increase the likelihood of precipitation, wasting the alkalinity solution and potentially stressing certain organisms, especially those without sufficient nutrients in the water.
Ways in which Alkalinity can Accumulate
There are several ways in which alkalinity can accumulate in a reef tank, some of which are more obvious than others.
Deliberate Dosing: One of the most straightforward ways to increase alkalinity is by adding an alkalinity supplement to the tank. However, it’s important to be careful not to overdo it, as this can lead to excessively high alkalinity levels. Some types of salt mixes, such as Instant Ocean’s Reef Crystals or Red Sea’s Coral Pro Salt, also contain higher levels of alkalinity. Water changes, while generally beneficial, can also contribute to rising alkalinity if not carefully monitored.
Source Water: The source of your water can also affect alkalinity levels. Depending on where you live, your tap water may have a high level of alkalinity to begin with. If you use a salt mix that also has a high level of alkalinity, and then top off the tank with tap water to replace evaporation, the resulting saltwater can have an unexpectedly high level of alkalinity.
Low-Demand Tanks: In tanks with low demand for calcium and alkalinity, the levels of these substances can gradually increase over time due to the dissolution of calcium carbonate in the sand bed. This is a natural process that can occur in tanks with low stocking levels, but it’s important to be aware of it and take steps to replenish the sand bed as needed.
Denitrification: Certain processes involved in denitrification, such as dosing vodka, vinegar, or sugar, or using a sulfur denitrator, can also lead to an increase in alkalinity. For every 50 ppm of nitrates depleted, you will add 2.3 dKH of alkalinity. However, it’s important to note that the nitrification process (i.e. the conversion of ammonia to nitrates) and the addition of nitrates through dosing do not affect alkalinity levels.
Deceptive Products: Unfortunately, some products on the market may be mislabeled or misleading, leading to unexpected increases in alkalinity. For example, Aquavitro’s OH balance claims to elevate pH without increasing alkalinity, but any hydroxide solution will dissociate and use CO2 to create carbonate and bicarbonate, which will increase alkalinity. Aquavitro’s “calcification” product, which is made from calcium gluconate, does not mention its effect on alkalinity, but bacteria will metabolize the gluconate and add alkalinity to the tank. Brightwell’s Boost pH+ claims to increase pH to desirable levels without increasing alkalinity, but it actually contains a buffer that raises both pH and alkalinity. It’s important to do your research and be wary of products that make exaggerated or false claims.
Preventing Unwanted Alkalinity Increases
So, how can you prevent unwanted increases in alkalinity in your reef tank? Here are a few tips:
Monitor your alkalinity levels regularly, and be sure to use a reliable test kit.
Be careful not to over-dose alkalinity supplements, and pay attention to the alkalinity levels in the salt mix you choose.
Consider using an RO/DI system to remove excess minerals and contaminants from your source water.
If you have a low-demand tank, be sure to regularly replenish the sand bed to compensate for the dissolution of calcium carbonate.
Research the ingredients and effectiveness of any products you plan to use in your tank, and be wary of exaggerated or false claims.
By following these guidelines, you can help ensure that your tank’s alkalinity levels remain within the optimal range and contribute to the overall health and well-being of your coral and other aquatic life.