The secret to keeping Acropora and SPS

rr orange passion

Nothing brings me more joy in this hobby than a large, happy, healthy, polyps out, growing, colorful sps coral. The key to this magnificent site is stability. It may seem so simple and it is in someways  and in many ways it isn’t. In dealing with stability I find the most important value to monitor in your tank is alkalinity. Stable and consistent alkalinity is my secret to keeping happy, healthy and colorful sps. In this article I will use the words acropora, acro, sps and hard corals interchangeably.

Id like to get a couple points out of the way in order to discuss alkalinity more in depth. If any of these remarks don’t align with your views id just like to point out this is what works for me.




In order to keep acro you will need the following. If your missing any of these Id stick the easiest to keep species.

Strong lights
Strong to moderate flow
Low Nitrates (0-5ppm)
Lower phosphates (0.1 -1.0)

We deal with a lot of reefers from many different experience levels. Among the newer reefers or those just starting to dive into hard corals, I find a lot of them have trouble keeping sps in the beginning. The number one cause I have found behind poor sps success is alkalinity. Too high, too low and fluctuations. So lets start with alk (short for alkalinity)


Acros are sensitive

Acros are very sensitive animals, but once you figure out how alk effects these animals, they are really no harder than any other coral to keep. The first thing you should do if you are looking to keep hard corals or are having trouble keeping them alive is to test your nitrates. If you had determined they are within range and meet the other criteria for keeping sps than test your alk. If your not currently testing your alk and having trouble it may be as simple as stabilizing your alk levels. If you are dosing and not testing alk this is also a problem. In my opinion, you should never dose anything to your reef tank that you are not testing for. Alk is vital to acro health and a component that is very easy to over shoot ; the consequences of over dosing can be catastrophic. I dont want to get into the science of alk but a simple way to think about is it is the fuel for acro. Your acros in a sense
“suck up” the alk. I’m sorry if I’m dumbing this down to much for the advanced reefers but this method of thinking has always worked for me. Alk is almost like a fuel and your trying to hit the sweet spot to make your acro say ‘mmmmmmmm’. Too little is no good, to much can be dangerous and swinging alk is the worst of all.


rainbow sps coral


I strive to keep my alkalinity at 7.5 dkh. There a few different ways to measure alk but I find the DKH scale easiest to understand.

The oceans are naturally 7.0 DKH. You may read on some forums of some reefers keeping their alk as high as 10, and even 11,12 and 13. I do not understand how they do it. I can tell you that if the alk in my system goes 10 I’m in deep trouble. It will cause sps to do something known as ‘peeling’. Its probably the absolute worst thing that can happen to your hard corals. Its basically the sps shedding its skin due to extreme stress. It can be near impossible to save a hard coral from dying once it has begun to seriously peel. Sometime fragging it will salvage some branches, but if it is a strong peel where the skin is floating away due the power head current, that acro is most likely not going to make it. This is often refered to as RTN or rapid tissue necrosis. There also exists STN, slow tissue necrosis by which the coral dies slowly.  Alkalinity problems are notorious for causing RTN.sps peeling
salifert test kit


So the first step in keeping acro is testing your alk. I recommend salifert test kits for all the testing of your aquarium but its by far the best for alkalinity. Its inexpensive, readily available, easy to perform and quick. The results are consistent which is also important. I always strive to keep my DKH at 7.5 similar to ocean conditions and recommend all of our customers to do the same. Its a safe number. Under low alk conditions you may experience slower growth and vice versa. With higher alk you can experience faster growth but its risky. Some hard corals can tolerate higher alk and others cant. Instead of experimenting with the life of the coral I play it safe at 7.5. Growth has always been good and no need to worry about which species can handle it.





IMG_5114To successfully keep acro you want to avoid alkalinity swings. What do I mean by swing? I mean a drastic jump or drop in numbers. For example a swing from 7.5 dkh to 9.5 dkh over 24 hours would be considered a large swing. The alkalinity rises to fast for acropora to adjust. It can shock them , cause them to lose color or even peel. It can be hard to remember sometimes these are all found in the ocean! And the oceans dkh does not swing. It may vary from ocean to ocean but it does not experience the swings we can experience in our reef tanks. The key here is to keep your alk as stable as possible. If you decide to keep your alk at 9 and do not have any ill effects that’s great. Everyone’s tank is different and consequently their alk levels. The number you keep it at is less important than keeping it stable. See what works for you and then stick to it. It may involve some trial and error and unfortunately cost you some hard corals. I always recommend starting with less expensive frags to test the waters before purchasing larger colonies. Once you have gained some experience in keeping them alive and growing them you can graduate to larger and more challenging species.


If your alk is low you need to dose, if its too high then dont dose. I’ll go over dosing in another article as it will need its own explanation as it relates to calcium.

High or low calcium wont kill your acro. High nitrates can kill them but generally they will lose color. Variations in Temperature and salinity can harm acro. I have found nothing more lethal however than unstable alkalinity. For me this is the number one issues I have encountered when trying to keep hard corals.

So the key here is stability. Avoid swing and keep alk the same. It promotes acro color, growth and overall health. Email if you are having trouble keeping acro and want some advice.

Reeftech Starburst Montipora
Reeftech Starburst Montipora


Here is a list of the easiest to keep acropora species if you would like try
Birdsnest (Seriatopora)
Slimers (yongei)

here are some suggestions for intermediate
secalemilipora coral

here is a list of some that I would avoid until you are successfully in keeping those above

smooth skinsIMG_2927

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