What Do White Tips On SPS Corals Mean?
Have you come home to white tips on your SPS corals and do not know what they are or what to do? From afar, it can be hard to make out if it's something we need to be concerned with. White tips form either from regular coral growth or they are burnt tips resulting from alkalinity spike or tissue necrosis.
When your SPS coral fragments arrive, they would have originated from a very different environment to your reef tank. SPS coral fragments originate from all over the world, experiencing different conditions like water quality and lighting. This means when you first introduce SPS corals to a reef tank they may change colors as they adapt to their new environment.
The issue we reef hobbyists have is that corals usually have specialized water chemistry, lighting, water flow, and feeding requirements, depending on what reef they originate from in the world. For example, corals from the Philippines may thrive in salinity levels of 32 ppt while corals from the Red Sea may thrive in 37 ppt. However, some corals of the same species can tolerate fluctuations in their environment before showing signs of stress like white tips.
We are still unsure if stress responses to water parameters such as salinity and alkalinity are due to physiological or evolutionary/ecological adaptations. However, what we do know is that such tolerances vary geographically, even with the same species of SPS coral.
If you notice your SPS corals turning ghostly white at the tips and are wondering why, do not fear, we have the answer you’re looking for!
Reasons For White Tips on SPS Corals
If you have noticed white tips on one or more of your SPS corals, the reasons for this are most likely:
Firstly, take a close look at your SPS corals. Are the white tips just the coral tips, or can you see white areas under the fragment tip or even at the base? If white tips are only visible on the branch ends and your water parameters are within range, then it’s most likely you have some awesome growth tips!
In addition, if algae is growing on the white tip, then it's likely dead tissue. Algae does not grow on living coral tissue. Dead tissue also does not look smooth like living tissue does.
If there are white areas on other parts of your SPS coral, and water parameters are not within the SPS coral-friendly range, then it is likely your SPS corals are suffering from burnt tips or STN.
If your SPS coral has burnt tips/alkalinity burn or STN, you will need to check the water chemistry, and possibly adjust the water parameters. When making any changes, ensure they are done gradually, as too many changes can cause problems to the healthy corals in your reef tank.
White tips on SPS corals can mean growth, which is a good thing! Often you will notice when diving there are white tips on corals, especially SPS corals such as Acropora. That is because white tips are not always a cause for concern....white tips can mean growth! If the white tips have polyps growing on and/or around them, then generally it’s a good sign.
As corals grow, the tips appear white due to active accretion of the calcium carbonate skeleton which create exposed areas on the coral fragments that are absent of zooxanthellae. It is the photosynthesis process of zooxanthellae in the coral polyp that enhances the calcifying rate of an SPS coral.
If you notice the white tips are getting larger and start traveling down the coral, then you are likely bleaching them. Turn down your lighting slowly; SPS corals thrive best in lighting between 200 and 450 PAR. However, this can change depending on the species of SPS coral you are keeping, so knowing the PAR for the particular species you have is critical.
Burnt tips occur when nutrient levels are too low and alkalinity rises too much too fast.
Burnt tips are usually shown with white tips, and the surrounding flesh will often look patchy as the tissue is lost around the coral's tips.
Always focus on alkalinity first, as any swing has to potential to kill your SPS corals faster than any lighting issues you may have. There seems to be a correlation between burnt tips and suddenly high alkalinity (9.0-10.0 dKH) in low nutrient systems. It's been speculated that corals do not have enough nutrients to grow its tissue at the same pace as its skeletal growth fueled by an elevated alkalinity level.
In some cases, burnt tips will resolve on their own. If you catch it early enough and make correction measure, corals can recover and start growing over the burnt tips. Or if you begin fragging off dead parts to save the colony, it's possible that the burnt tips will stop progressing.
Slow Tissue Necrosis (STN)
STN can take days to months to occur and is something you must take seriously if your SPS corals become infected. STN and RTN (rapid tissue necrosis) are both caused by microscopic protozoans that infect the coral’s tissues and skeleton. These protozoans thrive in an environment that's out of balance and unnaturally favoring their existence, such as a temperature spike.
Take a look at the base of the coral, does it have white areas? This combined with white tips is most likely STN, as it starts at the bottom, eventually reaching the branches. In most cases the SPS coral's tissues will start to expose the bone of the coral and algae will start growing on dead part.
STN infections can be spread in the water, which is why putting newly bought corals into quarantine for a few months is critical to reducing infections to neighboring corals and other marine organisms.
Remember, acropora corals are more prone to STN when water parameters are not ideal or if they are not receiving the correct lighting or number of nutrients.
Like burnt tips, sometimes STN will stop on its own, some may need a coral dip, and some will progressively get worse until the SPS coral has completely died. If you notice STN, start fragging off as much as you can, ensuring you only cut off parts that are not infected. Make the necessary correction after performing tests that will give you an idea of what has possibly gone wrong.
Water Parameters & White Tips on SPS Corals
It is important to check your reef tank’s water parameters closely. If you notice white tips on your SPS corals, be sure to focus on the following:
- Phosphates (PO4)
When PO4 is high, it can impede coral growth, especially SPS corals that require a little more care than other corals like LPS and softies. Healthy PO4 levels in a heavily stocked SPS coral reef tank should have a reading of <0.1 ppm.
Always aim for your nitrates to read between 5 and 10 ppm, and phosphates 0.03-0.08 ppm to reduce the chances of burnt tips and STN. When SPS corals do not get enough nutrients, their tissue growth cannot keep up with calcium carbonate deposition, causing the undesired white tips. Ideal alkalinity levels for SPS corals are 8.0 dKH, but between 7.5 and 9 dKH is usually fine for most SPS corals, ensuring that any changes inside that range are steady.
When keeping SPS corals, aim for calcium levels around 420 ppm as bad white tips can appear when calcium drops below 380 ppm.
If your reef tank parameters are stable, and you have identified the issue, you should test for alkalinity, phosphates, and consider possible temperature swing at the beginning. Allow time for the coral to recover. Too many changes within a short span of time, including large water changes, can cause them more harm as water changes can further swing the alkalinity.
If you notice your SPS corals have white tips, most of the time they are growth tips. However, be aware of burnt tips from alkalinity spike, and slow tissue necrosis (STN), as these types of white tips are not what a healthy SPS coral should look like.
Check your water parameters often to watch for fluctuations, as these can cause distressing white tips. Any changes you make in your reef aquarium should always be done gradually so the SPS corals are not subject to more stress.
If you have any questions about what lighting we use, what colorful SPS coral frags we have, or about white tips, please feel free to reach out to one of our team at POTO. We are always happy to help!
Good luck and happy reefing!