MetroKat's famous 'Katropora', (A. Subulata)

You've got a sweet setup. You watched over that cycle like it was a newborn, added the token clownfish, clean-up crew, and you've been eyeing those small polyp stony corals at the LFS. You finally bring home a pretty frag, find the perfect spot for it and glue it down. It looks great under those actinics so you can't wait to add more. The next day you go to see how the frag is doing and IT IS BONE WHITE! What happened?! You try again a couple of times till you figure you are cursed and can't keep SPS.

This series of articles will cater to someone who expresses interests in maintaining and keeping small polyp stony corals in their reef aquarium for the first time. These articles assume you know what a nitrogen cycle is and that your tank has been set up for as long as it takes to have completed that cycle at the minimum. We will talk about our personal experiences in keeping beautiful, healthy, and bright SPS. We've had failures too, and it took some degree of trial and error to be able to sustain SPS.


Arce's Green Acropora

Tank Maturity

You may have heard of a time requirement to be able to keep SPS. This time requirement is put in place to give your tank an opportunity to build up its biological filtration so that it can handle the bioload you intend to have. What does that mean?


Arce's Millepora

Bacteria is your friend. Whodathunkit?

New systems that are just starting, and have fully cycled, will only have enough of a bacterial population to get through their initial cycle. As you add fish, which adds waste from the food you feed, over the course of the next few months that bacterial population will increase to be able to process the added bioloads. Aside from converting wastes through the nitrogen process, bacteria are also consumed by your corals and are essentially food.

New systems are very clean. You may think this is a good thing as most SPS keepers rave about their ultra low nutrient systems (ULNS). The term ULNS refers to low concentrations of phosphates and nitrates. Coral care instructions specify low nitrate and phosphate levels as requirements, but there is a big difference between an established low nutrient system and a young tank.

An established low nutrient system has the necessary bacterial population and diversity to sustain corals. It will also have Dissolved Organic Compounds (DOCs) in the system which in turn feed the SPS corals and help maintain their health.

A young tank is nutrient starved in this regard. You might think you can just feed heavily, or stock a young tank with a few fish to produce these DOCs but that can lead to ammonia spikes and algae issues due to your system not being able to handle the added nutrients.

This is why time is important, to give your tank a natural way to boost its biological capabilities to handle livestock.


Metrokat's Jason Fox Setosa with a Blenny under actinics


If there is one secret recipe to keeping beautiful and healthy SPS corals—it is Stability. A new system will fluctuate in a variety of parameters. Your nitrogen cycle will continue to fluctuate until you reach your equilibrium in your bacterial population. The parameters that are affected by this are your ammonia, nitrites and nitrates. During this time you should not be putting any SPS in your system.

Alkalinity, is probably the most important element to keep stable. It can swing due to your system being new and still establishing itself, or due to the salt mix you use. Coralline encrusted rocks for example, suck up alk like crazy and a low alk salt mix will quickly deplete between water changes. If you have alkalinity swings, your SPS will show stress in some form, usually lack of Polyp extension (P.E.), necrosis and loss of color.

It is suggested to keep alkalinity between 7 to 11 Dkh, which will support SPS, but some coral keepers like us feel the range of 7.0-8.5 to be the sweet spot.

Through the calcification process, stony corals will consume calcium and alkalinity to create their skeleton. Magnesium also plays a role in that process. As they consume these elements, their respective levels in your system will lower and need to be replaced. This will lead to dosing and supplement requirements which we will also discuss at a later time. Right now you need to understand the fact that your levels need to remain rock solid (with some slight variations) to keep your SPS happy and healthy. A spike in your alkalinity can lead to burnt tips, necrosis, and browning. RTN presents itself as a bone white coral, here one minute, gone the next. STN can sometimes show up as whitening at the base that slowly crawls upwards, it can also show as peeling flesh that spreads.


MetroKat's Red Sea Max

From personal observations, we have noticed that alkalinity swings, at the lower end of the suggested spectrum, prove to be less harmful to SPS corals than a swing at the higher end. There can be several factors which contribute to this observation, but as of now we can only speak from our experiences as hobbyists, not scientists.

Aside from your alkalinity levels, your phosphates and nitrates are another important level to watch and maintain. Large feedings or inadequate nutrient export can increase both of these levels and each can result in browning, growth stagnation and tissue necrosis.

Stability, in all parameters, is the key to a successful SPS system. Though some parameters will not be as detrimental to SPS, for example a swinging calcium level; they are nonetheless important to maintain stable as they in turn can throw other levels off.

CONTINUE READING: SPS Corals for Beginners, Part 2


About Our Guest Authors

Arce: Name’s Justin Arce, known as “Arce” on forums. My experience in reefs has been short, with only two years experience. But my current tank, a standard 29 gallon, has proven to be a successful SPS reef. My addiction to sticks is obvious when looking at my tank... and especially when looking at my wallet.

MetroKat: Kat has been blogging and testing products for Marine Depot since 2014. Her current system is a 50G CAD Lights Artisan mixed reef with a custom hybrid light and the new Gyre. She was Tank of The Month on Nano-Reef in 2012, featured on Reef Builders, Marine Depot and recently won Most Creative Nano on Reef2Reef.