Success in a Reef: Magnesium

Success in a Reef: Magnesium.

          Foundation elements are so titled to emphasize their necessity. Within the three primary foundation element parameters we discussed in our prior blog, you’ll surely remember the passive Magnesium. This parameter is much easier to maintain than Alkalinity, because, while it is critical for the formation of a variety of structures, including the skeletons and shells of many corals and other organisms, it doesn’t fluctuate a lot, and when it does, they are rarely dangerous to organisms. Mostly, things just pull out what they need, as long as it’s there, utilizing magnesium to make things easier, and then a lot of it is released back into the water column, free of its Calcium carbonate bond. With fewer external factors affecting its stability, it’s quite easy to keep stable. Additionally, Magnesium, 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 Magnesium 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?

Fun Behaviors

Magnesium, in its most simple description, is the mechanism at which seawater holds its supersaturated ions in a stable state, and it is the third most concentrated of the major ions. Generally sitting at around 1300 ppm, with regional differences that correlate with salinity levels. Higher Magnesium levels are not known to accelerate coral growth but Magnesium does help to facilitate many processes, both biological and chemical, on a coral reef. The primary function of Magnesium in seawater is to allow critical building block components, such as Calcium, to exist in a supersaturated state, without precipitating out, allowing organisms such as corals and bivalves to pull from the water larger quantities of ions, such as Calcium Carbonate, bonded with Magnesium. Higher amounts of Magnesium encourage stronger coral skeletons, as well as increase coralline algae growth.

Stubborn Behaviors

The voice of the sea speaks to the soul. The touch of the sea is sensuous, enfolding the body in its soft, close embrace – Kate Chopin, is probably the best way to describe the stubborn behavioral properties of Magnesium, because there really aren’t many. Additionally, Magnesium is behind the scenes of everything going on underwater. Magnesium isn’t that tricky to manage, it’s just that, Magnesium’s greatest aspect is sometimes its greatest undoing: Magnesium is supersaturated in seawater, and because it enables other, more critical coral building ions to remain stable at similarly supersaturated level, a deficit can be a serious issue. This means that, given the correct circumstances, Magnesium will prevent the precipitation of Calcium and Alkalinity Compounds. Magnesium is truly the Soul of the Sea. This foundational component of biological and coral growth is going to be stable most of the time, with no problems. While there is a general range that is acceptable, or least likely to be problematic if kept stable (1250-1600ppm), there aren’t a lot of benefits to one particular area. We recommend allowing your tank to sit where it wants, when it comes to Magnesium, as long as it is high enough for you to feel comfortable that a small fluctuation won’t bring your aquarium below the safety range. There really aren’t too many pros and cons to different Magnesium levels, so we’ll discuss signs that your tank might have a imbalance, and 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 control.

Primary Benefit and Concern to Each

Magnesium, as we now know, is absolutely critical to allowing corals to grab the ions they need for coral skeletalgenesis (the process which corals build their skeleton) but we also understand it to be relatively stable and consistent all on its own. Magnesium is used by a multitude of organisms, for more reasons than we have learned thus far.

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 Magnesium better than others. Generally, however, most do pretty well. Magnesium doesn’t like to cause problems unless it is too low. A low magnesium is most likely to slow down coral growth, and weaken their skeletons over time.

As a general rule of thumb:

  • Soft Corals tolerate fluctuations the best. They don’t consume a lot of Magnesium or Calcium and so would take a long time to respond negatively to minor or even medium issues with stability. These corals are not likely to melt completely if a Magnesium fluctuation is too severe, or rapid, but will respond by closing up, reducing or pausing growth, or shrinking a bit, should the fluctuation be drastic or prolonged. They also 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 not very likely to respond negatively to long periods of fluctuations or very large fluctuations. LPS often grow very brittle skeletons if Magnesium is not high enough. A lot of them become so brittle you can crush them with your hand, while they are alive. 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. Most species can tolerate a fluctuation if it is short lived, and remains within the acceptable parameters. When it comes to SPS, they are all different. If stressed from Magnesium, 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, most likely with Magnesium issues) or rapid (RTN), and some will recede from their tips. The stress of a fluctuating Magnesium can cause them to melt away entirely if the problem is not corrected correctly, but this would require lengthy neglect.

General Differences

Below is a handy chart which you can use to get an idea of the primary benefit, and concern, of each end of the Magnesium range. Take a look at the notes under each section.

Magnesium – 1250 ppm Should not fluctuate more than 100ppm in 24 hours

Soft Coral 

LPS Coral 

SPS Coral 

High (1300+) * Overall benefit comes from improved stability a higher Magnesium provides.

Nominal Growth Rate.

Nominal Growth Rate.

Nominal to slight improvement in Growth Rate.

Low (900-1200 ppm) ** Not recommend for most systems – can cause precipitation issues & stunted growth rates

Nominal Growth Rate.

May reduce growth rate if Calcium or Alkalinity is not high enough.

Will reduce growth rate, and may lead to recession if kept too low, too long. Will also cause issues with precipitation and SPS are more sensitive to this.


Choosing a Magnesium Level

Now that we’ve discussed the differences in Magnesium levels, you’ll see there isn’t really much here to decide. Your salt mix will take care of this for you. Every brand is different, but when it comes to Magnesium, most are about the same. Choose a salt mix that works for your Alkalinity level only. You really only want to make sure your tank is close to whatever salt mix you choose for your Alkalinity, otherwise, each water change you do will cause an unnecessary fluctuation in your Magnesium level. As mentioned, your salt mix is vitally important to the stability of your aquarium, but I find it necessary to point out that anyone can be successful running any system they want using any reputable brand of salt,  but 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 Magnesium discussion, and all that remains is adjustment techniques, and you’re in luck, because it’s really quite simple.

  • If your Magnesium is low, and you are not already using a Magnesium buffing product, or a two-part buffing system, such as [Reef Fusion / Red Sea Foundation Elements Kit Link], 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 Magnesium 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. However, depending on where it’s at, it’s likely not any cause for concern. Most aquarists would not act on this alone.

In Conclusion… Magnesium is not so scary.

Remember earlier when we discussed choosing a salt mix that is around the Alkalinity level that you’d like your tank to operate at? Well, the second benefit this offers is the ability to correct your tanks parameters (all of them, really, but specifically here, Magnesium) 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 passive parameter is also one that wants to remain stable, doesn’t need fixing very often, and that means Magnesium really is the passive foundation parameter. 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


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