Success in a Reef: Alkalinity.
Foundation elements are so titled to emphasize their necessity. Within the three primary foundation element parameters we discussed in our prior Introduction to the Foundation Elements, you’ll surely remember the worrisome Alkalinity. This parameter is tough, because it can be affected by multiple things, and it can affect, multiple things. However, Alkalinity, much like the rest of your aquarium, wants to be stable, and consistent. What do I mean by ‘wants to be stable?’, I mean that you’ll only be have troubles when things go awry. With a proper testing, dosing, and maintenance schedule, you should not have to worry. Together, we’ll explore the components of Alkalinity and its primary behaviors, what that means for your reef tank, its dangers and how it fluctuates, how this affects corals and how they respond, and finally, we’ll go over some tips to keep it stable.
What Does it Do?
Alkalinity, in its most simple description, is an amalgamation of ions and compounds [in a body of water] and is represented as a measure of this concentration of ions. In the U.S., we typically report in dKH or ppm. Alkalinity is essentially your aquariums capacity to buffer acids, which directly controls the pH (acidity) of your water column. pH management is the prime directive of your Alkalinity parameter. For example, it is responsible for minimizing the natural pH swing that occurs as life underwater transitions from day-time to night-time, while also minimizing the likelihood other pH swings occur. And secondly, several of the components, namely Calcium Carbonate (Aragonite) and Bicarbonate, play a key role in every step of the coral biomineralization and skeletalgenesis process. There are several steps to each corallites development, and CaCO3 (Aragonite) is vital to each one, sometimes in a rotating manner (more on this in SIAR: Magnesium blog link), being utilized in numerous ways. With Alkalinity being so vital to coral growth, a higher Alkalinity level can actually be correlated to an increased growth rate in most species, providing it is being kept stable, as corals utilize the components by grabbing them out of seawater, and in turn, having a higher saturation (level) increases their ability to obtain what they need and want from the water column. Along with this, corals must have access to enough nutrients to support this artificially increased growth rate. Among growth benefits, higher Alkalinity levels also reduce the likelihood and effects of other parameter fluctuations.
You can’t stop the waves, but you can learn to surf! – Jon Kabat-Zan is probably the best way to describe the stubborn behavioral properties of Alkalinity, because it can sometimes act like it has a mind of its own. This truly foundational component of coral growth and management is going to be stable where it most makes sense, to the aquarium, using the combination of equipment and ecosystem choices to figure out what it wants to be, and in some aquariums, this means that you might just have to accept a parameter slightly higher or lower than you might like. While there is a general range that is acceptable, or least likely to be problematic if kept stable (7-12dKH), each with benefits and downsides, some aquariums will not be happy where others are. Additionally, aged systems sometimes show resistance when attempting to run lower Alkalinity levels (likely due to rapid dissolution of the substrate or rock, which can often times be resolved with a partial or full replacement to the sand bed) and newer, young systems sometimes show resistance to higher Alkalinity levels due to the utilization of fresh rock or substrate. Luckily, both of these cases tend to be rare, but provide a good illustration of how Alkalinity can operate. These behaviors can make it challenging to adjust or control Alkalinity levels because your aquarium is always going to look for a balance, and it sees everything. After we discuss the pros and cons of each end of the acceptable range, we’ll discuss management options. However, don’t worry too much, as your family over here at Blue Fish Aquarium, and the products we recommend, make it very simple, and easy to do so.
Primary Benefit and Concern to Each
Alkalinity, as we now know, is absolutely critical to coral skeletalgenesis (the process which corals build their skeleton) but because of this, it also makes it the most dangerous parameter to fluctuate.
In reef aquaria, we often categorize corals and reef systems into three general, unofficial groups:
- Soft Corals, which are corals that do not grow from a stony skeleton, often these are fleshy corals that cover preexisting reef structures and rocks. Example: Star Polyp, Pulsing Xenia, Leather Corals
- LPS Corals, (Large Polyp, Stony Coral) which are corals that grow from a skeleton, but usually cover it up with a much larger, usually single, Polyp. Example: Torch, Hammer, Acan, Chalice corals
- SPS Corals, (Small Polyp, Stony Coral) which are corals that grow from a skeleton and often have tiny or very, very small Polyps. Example: Acropora, Montipora, Seriatopora corals.
Some corals react to fluctuations in Alkalinity better than others. Generally, however, most do not take kindly to them.
As a general rule of thumb:
- Soft Corals tolerate fluctuations the longest. These corals can melt completely if an Alkalinity fluctuation is too severe, or rapid, but can usually handle small fluctuations that occur often or large fluctuations over shorter periods. If stressed from Alkalinity, they will remain closed up, and some will shrink a bit, before melting away if the problem is not corrected. They tolerate aggressive water change protocols well.
- LPS Corals, tolerate temporary fluctuations well, even if they are reoccurring or routine (like from water changes with salt that mixes higher than your tank.) These corals are very likely to respond negatively to long periods of fluctuations or large fluctuations, and can melt completely if the fluctuation is too rapid, or too large. If stressed from Alkalinity, they will remain closed up, and some will recede from their edges, before melting away if the problem is not corrected. They tolerate aggressive water change protocols well.
- SPS Corals, (Small Polyp, Stony Coral) which are considered the most sensitive group of corals. They deserve their name. Common species can tolerate minor fluctuations without issue but most SPS corals will respond negatively to most fluctuations. They are unapologetically unforgiving of reoccurring, or rapid fluctuations, and most species will not tolerate even one severe mistake. If stressed from Alkalinity, their polyps will not extend, or extend in patches, followed by a loss of color and/or recession on their growth edges. This recession will be either slow (STN) or rapid (RTN), and some will recede from their tips. The stress of a fluctuating Alkalinity causes them to melt away entirely if the problem is not corrected correctly.
Below is a handy chart which you can use to get an idea of the primary benefit, and concern, of each end of the Alkalinity range. Take a look at the notes under each section.
Alkalinity –Should not fluctuate more than .4 - .5 dKh in 24 hours. Natural Sea Water is understood to be 7 or slightly above 7 dKH
Soft Coral – Most are very forgiving of ALK Fluctuations.
LPS Coral – Most are forgiving of ALK Fluctuations.
SPS Coral – Most are very likely to die from continued ALK Fluctuations. Some species are more sensitive than others, and will react poorly every time.
High (10-12dKH) * Overall benefit comes from improved stability a higher Alkalinity provides.
Minor improvement in growth rate.
Medium improvement in growth rate. No effect on most LPS coral color.
Medium to Major improvement in growth rate, depending on species. Requires enough nutrients to support rapid growth.
Low (7-9 dKH) * Low Alkalinity must be accompanied with low nutrients to prevent skeletal recession / Causes tips to “burn” in SPS corals as nutrients support faster growth than available building block ions do.
Nominal affect to growth rate, few corals display higher vibrancy of color.
Nominal affect to growth rate, few corals display higher vibrancy of color.
Medium affect to growth rate, some corals faster, some slower, almost all display noticeably higher vibrancy of color. Note* SPS corals require strict nutrient management at low Alkalinity.
Choosing an Alkalinity Level
Now that we’ve discussed the differences in Alkalinity levels, this is the most important part of a serious reef tank ecosystem: You need to decide on an Alkalinity level, or general area (example: between 8-9), that you’d like to keep your reef tank. Once you decide on either the low end, or the high end, you can use this information to choose a salt mix that mixes as close to your desired level as possible. Every brand is different; there are low, medium, and, high range salt mixes at our store. For example, if you are seeking to run a low Alkalinity aquarium around 8.0dKH, the salt mix which you will have the highest probability of maintaining that successfully is Red Sea Blue Bucket, because a fresh batch of this saltwater, at a specific gravity of 1.026, will be around 8.0. You want to avoid using a salt mix that freshly mixes significantly higher or lower than your target. Otherwise, each water change you do will cause an unnecessary fluctuation in your Alkalinity level. In our previous example, at that low Alkalinity, we would strictly steer clear of Instant Ocean or Instant Ocean's Reef Crystals which each mix to the high range of 11-12. As you can see, your salt mix is vitally important to the stability of your aquarium, and whereas anyone can be successful running any system they want using any reputable brand of salt, choosing the right salt mix can make things a lot easier for you, and a lot less stressful for your corals and your aquarium in general.
More on this topic. Success in a Reef: Mixing Saltwater.
Tips for Adjusting
Finally, we’ve reached the end of our Alkalinity discussion, and all that remains is adjustment techniques, and you’re in luck, because it’s really quite simple.
- If your Alkalinity is low, and you are not already using an Alkalinity buffing product, or a two-part buffing system, such as Seachem Reef Fusion / Red Sea Foundation Elements Kit, then this is your first step here. A lot of times, a small amount is needed to keep things stable, especially as your aquarium begins to grow and mature.
- If your Alkalinity is too high, and you are looking to lower it, then you’ll want to refer to every aquarists easiest and strongest tool for most problems: Water changes with your chosen salt mix.
In Conclusion… Alkalinity is not so scary.
Remember earlier when we discussed choosing a salt mix that is around the level you’d like your tank to be at? Well, the second benefit this offers is the ability to correct your tanks parameters (all of them, really, but specifically here, Alkalinity) by doing water changes. Using the same salt mix each time will also give you a basic idea of what you can expect your tank to look like, and how you can expect it to behave, after a water change. Most aquariums have to do water changes anyway, so you may as well ensure your parameters are lining up how you want them at the same time. Using a salt mix with your ideal parameters will ensure this goes smoothly each time, and even allows you to do larger water changes, as there will be less dangerous fluctuations. So, never fear my friend, the scariest parameter has some very easy methods to fix, and that means Alkalinity might not be so scary after all. Couple this, with our help, and you’re in for a golden ride. Reef Aquariums have never been easier to set up, maintain, or enjoy, and we are here to help you, every step of the way.
Author: Sean L