How to speed up coral growth?

KH

The KH level (carbonate hardness) is a crucial parameter in saltwater aquariums because it directly affects the health and growth of corals. The optimal KH level ranges from 7 to 12 dkh. Maintaining KH in the higher range (10-12 dKh) can contribute to faster coral growth while helping to keep the water’s pH stable. Stable pH is important as it supports the photosynthesis process carried out by zooxanthellae, symbiotic algae living in corals, directly influencing their health and growth.

Circulation

Research conducted by Hughes et al. (2018) and Wangpraseurt et al. (2017) highlighted the importance of strong water movement for the health and growth of corals. Powerful water flow can alleviate physiological stress in corals, stimulate the photosynthesis of their symbiotic algae (zooxanthellae), and enhance their resilience to climate changes.

In saltwater aquariums, increased water circulation is crucial for supplying nutrients and aids in clearing corals of unwanted metabolic byproducts.

Lighting

Corals contain microscopic algae called zooxanthellae, living within their cells, conducting photosynthesis to produce carbohydrates and amino acids for the corals. In return, corals provide shelter and essential substances for photosynthesis. This process involves the absorption of light energy by chlorophyll in zooxanthellae, leading to glucose production.

The photosynthetic potential of corals depends on various factors such as the quality and intensity of light (PAR), water circulation efficiency, KH level, temperature, nutrient concentration, and appropriate chemical conditions. All these elements work together to enable corals to undergo efficient photosynthesis and achieve healthy growth.

When increasing light intensity, it’s important to consider enhancing water circulation.

Water temperature

Water temperature significantly influences the growth rate of corals. Reef aquariums and corals do not tolerate temperatures below 20°C (68°F), with the optimal range being between 24–28°C (75.2–82.4°F). While some species can tolerate brief exposure to temperatures up to 40°C (104°F), prolonged exposure to such temperatures can be harmful. For a saltwater aquarium, it is not recommended to drop below 23°C (73.4°F).

Research conducted by the Scripps Institution of Oceanography revealed that coral growth is highly sensitive to changes in water temperature. It was found that coral growth accelerates with increasing water temperature, but only up to a certain point. If the temperature becomes too high or rises too rapidly, corals quickly reach a critical point, beyond which their growth significantly slows down, leading to bleaching and potential coral death.

From a practical standpoint, as a marine hobbyist and someone who has managed a coral farm and store for some time, I can say that slightly higher temperatures, such as 27-28°C (80.60-82.4°F), tend to result in somewhat faster coral growth. However, these are personal observations, and as is common in saltwater aquariums, each tank is unique.

Appropriate pH

The role of pH in the saltwater aquarium ecosystem:

• pH indicates whether water is acidic or alkaline, which is crucial for many biological processes in the aquarium. 
• The optimal pH range for a reef aquarium is 8.1-8.4, influencing the solubility of nutrients in the water and speeding up the coral calcification process.

Effects on fish and coral health: 

• A stable and optimal pH is less stressful for corals, promoting their growth. 
• High pH has an antiseptic effect, destroying microorganisms on the skin, mucous membranes, and in infected fish wounds.

Impact on biological processes: 

• pH affects the nitrification process in a saltwater aquarium, where Nitrosomonas and Nitrobacter bacteria convert ammonia into nitrites and then into nitrates.

Take care of pH fluctuations in your aquarium:

• pH often fluctuates throughout the day, being higher during the day and lower at night due to coral photosynthesis and bacterial activity. 
• pH fluctuations can impact bacteria and nutrient concentrations in the aquarium, which is not favorable for corals.

Eliminate problems related to too low or too high pH: 

• Too low pH can lead to the release of sediment containing trace elements, including heavy metals, into the water. 
• Too high pH can cause damage to fish gills and kidneys, weaken their disease resistance, and inhibit growth.

Chemical balance

The topic of elemental balance in a saltwater aquarium is extensive, but in brief, it involves maintaining their levels at optimal values. Both too low and too high concentrations of minerals can impact the metabolic processes of corals, potentially leading to coral death. It’s important to note that each element can have a different impact on various coral species and even different effects on their biological functions. Additionally, there are dynamic relationships among elements present in seawater. When starting supplementation with trace elements, one should consider the complex interactions between them. For example, concentrations of elements like nickel (Ni), zinc (Zn), vanadium (V), copper (Cu), and molybdenum (Mo) are closely related.

However, at this point, let’s focus on achieving optimal levels to ensure that the elements are within the normal range, avoiding deficiencies or excesses, and preventing contamination by unwanted heavy metals. Regular testing and precise water composition control are essential to maintain a healthy and balanced environment for corals in a saltwater aquarium.

Nutrient Levels 

Lower nutrient values: 

• Positive Impact: Low levels of nutrients, such as nitrates (NO₃) and phosphates (PO₄), can have a positive effect on the health and coloration of corals, often resulting in brighter colors and better growth. Optimal levels of these nutrients may vary depending on individual aquarium conditions. For example, the optimal PO₄ level may be 0.08, and NO₃ – 0.5, but it’s important to adjust these values to your specific tank. Some aquariums may function well at higher levels, such as 0.15 PO₄. It’s essential to experiment gradually to find the ideal conditions for your aquarium.
• Risk: Too low nutrient levels can starve corals and their symbiotic algae (zooxanthellae), negatively affecting their ability to photosynthesize and grow. We aim to avoid levels of 0.

Excess Nutrients:

• Risk for Corals: High levels of nitrogen (as nitrates) and phosphorus (as phosphates) can lead to excessive growth of algae and cyanobacteria. Such an environment is harmful to corals because algae can overshadow them, limiting access to light and space.
• Effect on Coral Health: Excess nutrients can also reduce the intensity of coral colors, causing them to appear duller or brownish. This may be a result of an increased population of zooxanthellae in coral tissues, altering their appearance.

Stability

Stability in saltwater aquarium conditions is crucial to avoid stressing corals. Corals have limited adaptability to rapid environmental changes, so any modifications, such as nutrient levels, circulation, lighting, KH, salinity, and others, should be introduced gradually. Sudden parameter jumps can cause significant stress to corals. Maintaining a consistent, repeatable pattern of conditions in the aquarium is essential for the healthy growth of corals. Sudden changes can hinder their development, making a consistent and calm approach to parameter regulation crucial.

Synergy of areas

Once we have established the right nutrient levels, water chemistry, pH, temperature, and KH, we can gently increase the coral growth rate. We begin by enhancing water circulation, which is the first step. Next, in the subsequent stage, we gradually boost the lighting. After that, we can slowly raise the KH level to further support faster coral growth.

Increasing water circulation, lighting, or raising KH requires close monitoring of KH, Ca, and Mg levels, as these changes can occur rapidly. If consumption increases, we need to adjust the dosing in time (we don’t want aquarium parameters to destabilize, leading to coral stress, which hinders growth).

Automatic testers, such as KH keeper Plus, can be helpful in this process. If consumption starts to rise, it’s a good sign. The calcification process has accelerated, and corals will grow faster.

It’s also essential to monitor the PO₄ level, which may require adjustments in response to changes. In my case, PO₄ decreased by a few points within a day, for example, dropping from 0.08 to 0.06. I increased dosing on pumps to make it rise by 0.01 per day.

To ensure optimal conditions for coral growth, we first focus on aquarium stability, proper water chemistry, and appropriate nutrients. Then, we increase water circulation and PAR light intensity, and in the next step, gradually raise the KH level. We monitor KH and PO₄ (and occasionally check Ca and Mg) to adjust the dosing of components and PO₄ fluid, which will likely be consumed at a higher rate.

Summary

Managing the PO₄ level was a significant challenge for me as it influenced the rate of mineral consumption in the aquarium (monitored based on KH keeper and the assumption that everything is consumed in equal proportion). I worked on finding a balance between key aspects: stronger water circulation, quality PAR light, and a higher KH level (done in the second stage). Each of these elements is increased individually, starting with circulation, which is crucial for better coral metabolism. Even while maintaining KH at the standard level of 8 dKh, I observed an increase in component consumption and faster coral growth.