Coral grows so slowly that the question of how fast it should grow becomes a concern. The growth rate for new reef tanks on a day-to-day basis is so incremental that you aren’t likely to see that it’s happened. That may leave you wondering if your coral is growing at all.
In ideal conditions, branching and staghorn corals have the potential to grow up to eight inches (20 cm) per year in a home reef tank. Massive corals, on the other hand, grow only up to an inch (25 mm) per year. Soft corals grow faster, whereas non-photosynthetic corals are slower.
Read on to learn how you can tell if your coral is growing, even though you can’t see it day-to-day. I’ll suggest some ways to speed up the growth of your coral. I’ll also talk about why your coral may not be growing and what to do about it.
How Fast Does Coral Grow in a Reef Tank?
Coral in a reef tank often grows slower than it would in the ocean. By duplicating ocean conditions, you can ensure that coral grows at the fastest possible rate. However, branching and staghorn corals only grow up to an inch per year, whereas massive corals grow more slowly.
When asked “how fast does coral grow?” in a forum, one member quipped that the correct answer was “not fast enough.” Probably can’t disagree with that. All corals grow slowly, though, so calling a coral a fast grower means it’s faster than other corals.
Nevertheless, soft corals, or softies, are the fastest-growing corals. Unlike stony corals and non-photosynthetic corals, soft corals don’t form external skeletal structures. Instead, they have sclerites which are small, needle support structures.
Of the two types of stony corals, Large Polyp Stony Corals (LPS) and Small Polyp Stony Corals (SPS), LPS corals are easier to grow. SPS corals require very stable tank parameters to be maintained. Variations in those parameters can slow or stop the growth of LPS corals.
Non-photosynthetic corals (NPS) have the fussiest requirements for feeding and tank parameters. These are the slowest-growing corals in any case. As with LPS corals, though, variations in feeding and tank parameters can slow or stop growth.
Overall, to host coral, invertebrates, and fish, you’ll need to establish a nitrogen cycle that shows it has a colony of bacteria that can neutralize ammonia buildup. After the nitrogen cycle is established, you can begin slowly adding corals and other residents.
Adding your coral, invertebrates, and fish a few at a time allows the filter of the nitrogen cycle to adjust to the increase in ammonia produced by the new inhabitants. Allowing this balance to re-establish itself helps prevent your reef tank from crashing and causing everything to die.
Unfortunately, when you reach this stage, you can expect your tank to look as if nothing has been happening for about 12 to 18 months. One reason is that if you have LPS, SPS, or NFS corals, they will be building their skeletal support structure before they begin to grow.
When you begin to see coralline algae appearing on the surfaces in your reef tank, you’ll know that your tank has matured. You can now expect more rapid growth from your coral. Reaching this stage can take 18 to 24 months.
Is Your Coral Growing? How to Find Out
The easiest way to tell if your coral is growing is to take a photo of your reef tank once a month. As I’ve said, coral grows so slowly that you probably won’t notice the difference on a day-to-day basis, but the difference you’ll see from month to month should surprise and please you.
There is also another way to test whether or not your coral is growing. You measure the dKH level or the alkalinity of the water. Alkalinity and dKH are the same things.
The dKH level for the water in your reef tank should be 8 to 12 dKH or 142 and 215 ppm.
The alkaline level indicates the level of calcium carbonate in the water. Your LPS, SPS, and NPS corals use calcium carbonate to build their exterior skeletal structures. So, if your corals are growing, you should see those levels drop when you test the dKH levels every week.
However, your coral can maintain its color even if it does not take in calcium carbonate and grow. It can enter a maintenance phase as it waits for improved conditions that allow it to grow.
Suppose you’ve had your reef tank’s lighting set to a 10-hour schedule. If the dKH level drops week to week, then you can continue that schedule. But if the dKH level isn’t falling, try changing the light to a 12-hour schedule.
Your coral has started to grow if the dKH level begins to drop after changing the light schedule. You’ve simply haven’t been exposing it to light for a long enough period.
If the dKH level still isn’t dropping, either your PAR or your lighting system’s spectrum isn’t providing your coral with the right intensity or wavelength of light.
Why Isn’t Your Coral Growing?
Some reasons why your coral isn’t growing include improper alkaline levels, light and PAR levels, and water flow direction and rate. Changing bulbs when they’re eight months old, adjusting lighting schedules, and not using tap water can help your coral grow.
I’ve already discussed alkaline levels and light. The amount of light needed by your coral is the PAR measurement. The other factor that influences coral growth is the rate and direction of the water flow in your reef tank. To ensure your coral grows, you should maintain these levels.
Alkaline levels should remain stable to ensure that your LPS, SPS, and NPS corals have a consistent supply of calcium carbonate. If your dKH levels rise and fall week to week, your LPS, SPS, and NPS corals will alternate between periods of growing and not growing.
The wavelength and intensity of light your coral needs depends on the ocean depth native to the species.
Corals from species that grow at shallow depths need more intense light covering more of the full spectrum of white light. Corals that grow at greater depths need less intense light with more light in the blue range of the spectrum, duplicating the filter created by ocean water.
Photosynthetic Useable Radiation (PUR) Levels
Orphek Aquarium LED Lighting explains Photosynthetic Useable Radiation (PUR) levels.
Because NPS corals don’t depend on photosynthesis, they are less affected by your reef tank’s light source. But according to TheBeginnersReef.com, soft, LPS, and SPS corals get 95 percent of their energy from photosynthesis.
Organisms called Zooxanthellae that are contained in the tissues of soft, LPS, and SPS corals have three types of chlorophyll or Clades — chlorophyll A, chlorophyll B, and chlorophyll C. Each type, or Clade of chlorophyll, responds to a different wavelength of light.
Corals depend most on photosynthesis from Clades A and B.
Clade A is most prominent in the tissues of your corals, and it responds to light from the blue end of the spectrum ranging from 450 to 550 nm (nanometers).
Clade B responds to light from the spectrum’s yellow, orange, and red wavelengths ranging from 620 to 700 nm.
Depending on whether you have LED lighting or a T5 or metal halide (MH) fixture, your lighting system will have either diodes or bulbs that produce light in the correct wavelengths.
Photosynthetic Available Radiation (PAR) Levels
PAR levels measure the brightness or intensity of the entire spectrum of visible light from 400 to 700 nm. Your light fixture should have a diagram showing you how much light your corals receive at different depths and distances in your reef tank.
In general, corals from species that grow in deeper ocean waters prefer low-level light at a PAR between 50 and 100. Corals that grow at somewhat shallower depths prefer a light intensity between 100 and 200. Corals from shallower waters prefer light in the 200 to 500 PAR range.
The rate and the direction of the water flow in your reef tank both matter to your coral’s growth. Coral growing in the ocean experiences the ebb and flow of the tide and may feel changes produced by the direction of the wind. The depth affects how much water flow coral feels.
Just like the flow of ocean water, the flow in your reef tank carries food to your coral. It also helps them with respiration by bringing oxygen to your coral and carrying carbon dioxide away. Finally, the flow of the water carries away digestive waste products.
The water in your reef tank should not flow directly at your coral but around it. And the direction of the flow should change randomly. You can accomplish this in two ways:
- You can direct the flow from your powerheads along the surface of the water. This duplicates the effect of wind-blown ocean water.
- You can create flow patterns of short and/or long pulses below the surface with a team of multiple controllable DC powerheads. These patterns can duplicate how the effects of tides and winds are felt at various depths of the oceans.
Current.com explains how to re-create ocean wave patterns.
The flow rate you should choose depends on the volume of your reef tank and the ocean depth that is native to your various species of coral. The deeper in the ocean your coral grows, the less they feel the movement in the water and lower the flow rate they will prefer.
- SPS corals prefer the highest rates of flow. For these corals, multiply the volume of your reef tank by a factor of 20 to 100.
- LPS corals prefer a low to moderate flow rate. Multiply the volume of your tank by a factor of 10 to 15.
- Soft corals prefer a low flow rate. Multiply the volume of the reef tank by a factor of 10.
Measure the flow rates in various parts of your reef tank and place your corals accordingly.
Other Factors That Inhibit Coral Growth Rates
Pest, crabs, stings from another coral, or diseases like brown jelly disease or tissue necrosis may explain why one coral has stopped growing. If one coral is stinging another, move the culprit at least 8 inches (203.2 mm) from its victim.
If you’re having trouble growing all of the coral in a particular species, thoroughly research the care requirements. Look for a parameter or parameters in your reef tank that you need to test and adjust the position of those corals, their feeding, or other factors to correct the problem.
If none of your corals are growing, check the alkaline levels, lighting, and flow in your reef tank first. If all of those are in the correct range for your corals, then try the following:
- Replace the bulbs in your lighting fixture if they’re more than eight months old. As time goes on, bulbs lose their power and efficiency.
- Don’t split your lighting schedule by turning the lights off when you’re at work and running them only when you’re at home getting ready for work and after you come home from work. Leave the lights on in a solid block of time to duplicate the way your coral would receive light in the ocean.
- Don’t use city water directly from the tap. City water goes through a filtration process that makes it safe for humans, but it’s not pure enough for coral. Install a quality RO/DI water filtration system for your reef tank.
- Check the levels of phosphates and nitrates in your reef tank. If the levels are off, they may need adjustment.
- The Zooxanthellae in your coral need a trace amount of phosphate and a nitrate level below 5ppm to grow. Keep track of these levels to ensure proper growth.
- Soft corals need phosphate levels of 0.03 ppm, and LPS corals need phosphate levels of 0.05 ppm. Higher amounts of phosphate inhibit growth in Zooxanthellae and calcium intake in other corals.
- Be certain that the filtration system that removes excess food, digestive wastes, and other material from your reef tank is the right size. If any of your equipment is too small, it won’t perform well enough, and the health of your coral will suffer for it.
- If your coral bleaches out after a light upgrade, reduce the time your lights or the intensity of the lights. Then gradually expand the time or increase the intensity to re-acclimate your coral.
- If your coral is turning brown, it’s not receiving the right quality or intensity of light. Extend the time you leave your lights on, lower your light fixture closer to the water, or use two light fixtures. If nothing improves, upgrade to a higher-quality light source.
If you’re looking for a small reef tank for a small space or a small apartment, consider the 29-gallon Coralife LED Biocube Aquarium from Amazon.com. This nano tank features a rear chamber that holds the pump, the filtration media, and adjustable flow nozzles.
The Biocube’s LED lighting can be set to duplicate the blue end of the spectrum or include more light from the yellow, orange, and red wavelengths. The timer enables you to adjust the amount of time you have your lights on. Users are growing soft and LPS corals with SPS corals on top.
Can You Speed up the Growth of Your Coral?
You can speed up the growth of your coral by upgrading your lighting and water flow system, adjusting your maintenance schedule, adding fish, and ensuring that the nutrient levels are ideal. In addition, you can feed the coral.
Follow the guidelines in the section about why your coral might not be growing. A regular testing and maintenance schedule provides the best conditions.
You knew I was going to say that, right?
If you covet someone else’s tank, shame on you! Stop coveting! Instead, ask them about their equipment, their maintenance schedule, and everything else about their tank. Then consider how you might apply what they’ve done to your own tank.
Upgrade your lighting and your water flow system.
If you have a reef-only tank, consider adding fish. Corals love gorging on fish poop.
You can also feed your coral, especially if you want an all coral reef tank with no fish.
Reefbuilders.com has a tip for speeding up new reef tanks. Cycling refers to building up the nitrogen cycle to prevent ammonia buildup. But coral isn’t harmed by ammonia, and it doesn’t cause it to build. So, start your coral while you’re cycling your tank.
Contrary to the recommendation to not split your light schedule, a Reef2Reef forum thread entitled Accelerated Coral Growth Tips cites environmental scientific research supporting the practice.
The first post in the Reef2Reef forum thread explains researchers found that a four-hours-on-eight-hours-off-four-hours-on light schedule increased growth. Read the thread before trying this.
You can find the study, “Motility of zooxanthellae isolated from the Red Sea soft coral Heteroxenia fuscescens (Cnidaria)” at ScienceDirect.com.
Deutsche Welle (DW) offers an idea from the 2018 start-up company Coral Vita.
Coral Vita restores and creates coral reefs for hotels, the wealthy, and others. The company speeds growth by breaking polyps apart, spacing them out, allowing them to fuse, and breaking them apart again.
I’ve also written an article on this topic on my website, which can be found here.
In summary, thoroughly research each coral currently in your tank.
Learn the wavelengths and intensity of light, and the water motion these species experience at the depth they are found in their natural ocean environment.
Adjust your lighting system and water flow to duplicate the ocean conditions each of your corals prefer. A successful reef tank depends mainly upon consistently maintaining the most favorable conditions possible.
You can also supplement your coral’s “diet” by adding minerals to your reef tank’s water. Orphek Aquarium LED Lighting suggests adding calcium, magnesium, strontium, potassium, and iron to improve both color and growth.
- The Beginner’s Reef: Why Are Your Corals Not Growing
- Current: How to Choose the Best Flow Mode for Your Aquarium Wave Pumps
- Deutsche Welle (DW): Making coral grow 50 times faster than nature
- Orphek Aquarium LED Lighting: About Corals
- Orphek Aquarium LED Lighting: How to Determine if Corals Are Growing
- Reef2Reef Forum: Accelerated Coral Growth Tips
- Reef Builders: Ask ReefBuilders #3: How Long Should I Cycle a Reef Tank Before Putting Corals In
- Science Direct: Motility of zooxanthellae isolated from the Red Sea soft coral Heteroxenia fuscescens (Cnidaria)