Reef alkalinity is misunderstood by many new keepers. It’s not about chasing specific values (as if there were a number) as much as it’s about stability. Rather than guesswork, this chart will help you match the life you keep to chemistry. Specifically, you’ll see that different coral types thrives in specific zones, not some single range.
Alkalinity act like a buffer against changes in your pH. As corals grows skeletons, they use up carbonate ions, which reduces your buffer capacity. Without those ions the pH drop. Corals then bleach, so you has to add carbonate ions to prevent that from happening.
Why Stability Is Important for Your Reef
The chart provides “health” zones, colors ranging from ideal through dangerous low; showing what’s good for keeping corals happy and healthy. Delicate branching corals require more alk than soft corals. Different type of corals require different things; don’t treat all tank alike or you’ll fail.
But to do well, you must test correctly. You need a quality kit with half-point accuracy. You don’t want those cheapie strips or low res kits that is all over the place. Professional grade will give you half-point resolution, which is enough to notice slight changes but not big enough to cause a crisis. Knowing the difference between 8 and 8.5 dKH is a small thing, but it can be the difference between steady growth and stalling out. On a serious setup, you’ll know why, because of your accurate testing and the ability to distinguish 8 dKH from 8 point 5 dKH. That makes a difference on expensive livestock.
Magnesium is part of a system with Alkalinity and Calcium. They is all interrelated so you can’t increase one without messing up another. Magnesium helps prevent carbonate ions (alkalinity) and calcium ions from precipitating out as dust in your tank. When magnesium gets really low, it makes the alk unstable because those chemicals will react with each other. So if everything else isn’t holding stable when you dose, look to magnesium first. Look at the grid for extreme swings causing toxicity or precipitation.
Tanks are not all the same. Ultra low nutrient SPS tanks needs stricter control and fewer daily changes, whereas fish only systems can handle larger changes. Use infographic to determine if you should of be testing every day, once per week, etc. Starting out most people begin with a LPS dominated tank since it handles larger fluctuations moderately well. As you incorporate more sensitive corals your precision of testing and how frequently you do it increase.
The number one rule for reefs: keep it stable. Corals adjust their internal chemistry to match their environment. Even if the average values are right, daily fluctuation are chronically stressful. Automation supports this by delivering smaller, more frequent doses instead of large daily doses that create highs and lows. Over time logging your results will show trends before it’s too late (ie, before you see problems). Ideally we want to achieve a steady state where the corals don’t have to worry about surviving and can simply grow.
