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Saltwater Setup: How Does a Reef Aquarium Work?

So, you've decided to dive into the mesmerizing world of saltwater aquariums, bringing the beauty of the ocean into your own home. Congratulations! Saltwater tanks offer a vibrant and lively aquatic environment that can be enjoyed with or without fish. However, adding saltwater fish elevates the experience to a whole new level.

Before making any purchases, it's crucial to understand how to construct and operate a saltwater aquarium. To assist our valued customers, we've conducted extensive research on the requirements for maintaining a fish with a live rock saltwater tank.

Review these pages catered to ensure full control and knowledge of you new reef system from us to you:

Saltwater Setup: How Does a Reef Aquarium Work? (current page)

Saltwater Setup: What Equipment will be Needed?

Check out the link to explore the different saltwater options (Saltwater Aquariums).

Creating a balanced and thriving reef tank is an art and science, aiming to replicate the intricate and stable environment of natural coral reefs. In the vast ocean, the water chemistry is remarkably stable, providing consistent levels of essential elements and compounds that marine life relies on for growth, health, and reproduction. These include major elements like sodium, chloride, magnesium, calcium, and potassium, as well as trace elements like iodine, iron, and zinc.

In a reef tank, the closed system doesn't benefit from the ocean's natural replenishment of these elements, so it's up to the aquarist to maintain these levels through various means

How Does a Reef Aquarium Work?

These parameters are what will go into creating a reef ecosystem:

  1. Providing Saltwater
  2. Temperature Control
  3. Lighting
  4. Flow & Circulation
  5. Filtration
  6. Replenishing elements

1. Providing Saltwater 

ensuring your reef tank has the right type of water is fundamental to the health and success of your marine ecosystem. Let's explore the two primary methods you mentioned for providing saltwater to your aquarium: purchasing pre-mixed saltwater and making your own saltwater using reverse osmosis deionization (RODI) water.

Buying Pre-mixed Saltwater

Many local fish stores or pet stores offer pre-mixed saltwater, which is convenient and ensures a certain level of consistency in water quality. This option is great for hobbyists who might not have the time, space, or desire to mix their own saltwater. However, it's essential to purchase from reputable sources to ensure the water is of high quality and free from contaminants that could harm your reef tank. Also, transporting large amounts of water can be cumbersome and might not be practical for everyone.

Mixing Your Own Saltwater with RODI Water

This method involves a bit more initial setup but offers greater control over the water quality and can be more cost-effective in the long run, especially for larger tanks or multiple aquarium setups.

  • Reverse Osmosis Deionization (RODI) System: This system filters tap water, removing chlorine, chloramines, heavy metals, and other impurities, as well as reducing the total dissolved solids (TDS) to near zero. This process ensures that the base water used to mix with the reef salt is as pure as possible, preventing unwanted algae growth and ensuring the health of the tank's inhabitants.
  • Mixing Saltwater: After obtaining RODI water, the next step is to add a marine salt mix to the water, following the manufacturer's instructions to achieve the desired specific gravity, usually around 1.025 for a reef tank. It's crucial to mix the saltwater thoroughly, ensuring all the salt is completely dissolved before adding it to the tank. Using a refractometer or hydrometer to measure specific gravity/salinity is essential to ensure the correct levels are achieved.
  • Aeration and Heating: Once mixed, it's beneficial to aerate the water and bring it to the appropriate temperature before adding it to your aquarium. This can be done by using a powerhead for circulation and a heater, if necessary. This process helps to stabilize the water, ensuring it's ready for your tank's inhabitants.

Considerations for Both Methods

Regardless of the method you choose, regular testing of your aquarium water is vital to monitor and maintain the correct levels of salinity, pH, alkalinity, calcium, magnesium, and trace elements. Adjustments should be made based on these test results to keep your reef tank thriving.

By either buying pre-mixed saltwater or mixing your own with RODI water, you can provide a healthy and stable environment for your reef tank's inhabitants. Each method has its advantages, and the best choice depends on your specific situation, preferences, and the needs of your reef aquarium.

 2. Temperature

Maintaining a stable temperature within the ideal range of 25-26°C (77-79°F) is crucial for a home reef aquarium. Natural coral reefs thrive in stable temperature conditions, which support the complex life cycles and metabolic processes of corals and other marine organisms. In the home aquarium, mimicking these stable conditions helps ensure the health and vitality of the ecosystem.

Why Temperature Stability Matters

  • Metabolism: Temperature significantly influences the metabolic rates of marine organisms. If the water is too cold, their metabolism slows down, affecting growth and immune response. Conversely, too warm temperatures can lead to increased metabolism, potentially causing stress, more rapid depletion of dissolved oxygen, and increased susceptibility to diseases.
  • Coral Bleaching: Elevated temperatures can lead to coral bleaching, where corals expel the symbiotic algae (zooxanthellae) living in their tissues, causing the coral to turn white and significantly reducing its energy source. Prolonged bleaching can lead to coral death.
  • Oxygen Levels: Water holds less dissolved oxygen at higher temperatures. If the aquarium water becomes too warm, it can lead to lower oxygen levels, stressing aquatic life.

How to Maintain Stable Aquarium Temperatures

  • Aquarium Heater: An adjustable aquarium heater is essential for maintaining a stable temperature within the desired range. Heaters come with built-in thermostats that turn the heater on and off to maintain the set temperature. It's a good practice to have a backup heater or an alarm system in place in case the primary heater fails.
  • Cooling Methods: In warmer climates or during hot seasons, aquarium temperatures can exceed the desired range. Fans blowing across the water surface or a dedicated aquarium chiller can help cool the water. Evaporative cooling (from fans) is more energy-efficient but requires topping off the evaporated water with fresh RODI water to maintain salinity levels.
  • Regular Monitoring: Digital thermometers or aquarium controllers can be used for continuous temperature monitoring. Some advanced systems can control both heaters and chillers, automating the process to maintain stable water temperatures.
  • Room Temperature: Keeping the room where the aquarium is located at a stable temperature can also help prevent large swings in water temperature. Avoid placing the tank near windows where it might receive direct sunlight or near vents that could cause rapid temperature changes.

Maintaining stable temperatures in your reef tank not only supports the health and well-being of its inhabitants but also contributes to the overall success and longevity of your marine ecosystem. Consistent monitoring and the right equipment are key to achieving this stability.

 3. Lighting

Corals have a symbiotic relationship with zooxanthellae, microscopic algae that live within their tissues. These algae perform photosynthesis, converting light energy into chemical energy, which provides the majority of the nutrients corals need to thrive. Indeed, it's estimated that up to 85% of a coral's energy needs are met through photosynthesis, highlighting the critical role of lighting in a reef aquarium.

Importance of Blue and Violet Light

  • Wavelengths: The specific intensities of blue and violet light (ranging roughly from 400 to 500 nanometers) are particularly crucial for photosynthesis in zooxanthellae. These wavelengths penetrate water more effectively than others, reaching corals at various depths in the ocean, which is why corals are so responsive to these parts of the light spectrum.
  • Penetration and Spread: High-quality reef aquarium lighting systems are designed to not only provide the right wavelengths but also to ensure that light penetrates evenly across the entire aquarium. This is important for reaching all corals, including those placed at the bottom or in shaded areas.

Choosing the Right Lighting for Reef Aquariums

  • LED Lighting: LED (Light Emitting Diode) lights are among the most popular choices for reef tanks due to their efficiency, longevity, and the ability to customize the spectrum of light they emit. Many LED systems allow aquarists to adjust the intensity and color of the light to mimic natural lighting conditions found in coral reefs, including the crucial blue and violet wavelengths.
  • Intensity and Duration: The intensity (or PAR, Photosynthetically Active Radiation) needs to be strong enough to reach the bottom of the tank and support photosynthesis in all corals, regardless of their placement. The duration of the light cycle also matters; a typical daylight cycle of around 8-12 hours mimics natural conditions and supports healthy coral growth.
  • Spread: The distribution of light is important to ensure that all areas of the aquarium receive adequate lighting. Advanced LED systems often feature lenses or reflectors designed to disperse light evenly, preventing hot spots where light is too intense and shadows where it's insufficient.
  • Cooling Systems: Because powerful lights can generate significant heat, many lighting systems are equipped with fans or other cooling mechanisms to prevent overheating both the lights and the aquarium water.

Monitoring and Adjusting Lighting

Adjusting and fine-tuning lighting conditions is an ongoing process in a reef aquarium. Aquarists should monitor coral health and growth as indicators of whether the lighting conditions are optimal. Signs of insufficient light may include slowed growth or corals becoming elongated as they reach towards the light source. Conversely, too much light can cause bleaching or the corals to expel their zooxanthellae. 

4. Water Flow & Circulation

Water flow and circulation are indeed pivotal in a reef tank, serving multiple roles that are essential for the health and well-being of corals and other tank inhabitants. Despite corals being sessile (non-moving) organisms, in their natural habitat, they rely on the constant movement of water to meet their physiological needs. Here’s why water flow is crucial in a reef aquarium:

Nutrient Distribution

Water movement is essential for distributing nutrients throughout the aquarium. Corals depend on the water flow to bring them phytoplankton, zooplankton, and dissolved nutrients, which are their primary food sources. Without adequate flow, these nutrients might not reach all corals equally, especially those located in lower flow areas.

Waste Removal

Just as water flow helps deliver nutrients, it also plays a crucial role in waste removal. Currents carry away the waste products produced by corals and other organisms, preventing the accumulation of detritus, which can lead to poor water quality and increased levels of nitrates and phosphates. Efficient water circulation ensures these waste products are directed towards filtration systems, where they can be removed from the system.

Mimicking Natural Conditions

In the ocean, corals are accustomed to varying flow conditions depending on their location. Some corals thrive in high-energy environments with strong currents, while others prefer more gentle flows. Replicating these conditions as closely as possible can help corals to exhibit natural growth forms and behaviors. Moreover, the water flow helps to strengthen coral structures over time, as they adapt to their environment.


Water movement is integral to oxygenating the water column. As water flows, it encourages gas exchange at the water's surface, increasing the dissolved oxygen levels essential for all aerobic organisms in the tank. Additionally, it helps to prevent the formation of low-oxygen microenvironments within the tank, which can be detrimental to the health of both corals and fish.

Preventing Algae Buildup and Detritus

Adequate water flow discourages the accumulation of algae and detritus by keeping these particles suspended in the water column, where they can be more easily captured by mechanical filtration. This not only helps in maintaining cleaner substrates and rockwork but also promotes a more aesthetically pleasing and healthier tank environment.

How to Achieve Proper Water Flow

Achieving the right water flow in a reef tank typically involves the use of powerheads, wave makers, and return pumps from sump filtration systems. The goal is to create a varied flow that reaches all parts of the aquarium without creating overly turbulent areas that might stress corals or other inhabitants. It’s often beneficial to use controllable pumps, which can simulate natural flow patterns including tidal flows and random currents.

It's important to observe the behavior and health of your corals and adjust the flow accordingly. Signs of too much flow might include corals retracting their polyps or being physically damaged, while too little flow can be indicated by excessive accumulation of detritus on corals or the tank floor.

5. Filtration

In a reef tank, maintaining pristine water quality is crucial for the health of corals and other marine inhabitants. This goal is achieved through a combination of mechanical, biological, and chemical filtration, each serving a unique role in the overall filtration process. Let's delve into each type:

1. Mechanical Filtration

Mechanical filtration involves physically removing particulate matter from the water, such as detritus, uneaten food, and waste products. This is typically the first stage in the filtration process, as it prevents the accumulation of organic materials that could decompose and deteriorate water quality. Common mechanical filtration methods include:

  • Sponge Filters: These trap particles as water passes through them. Sponges need to be cleaned regularly to prevent them from becoming clogged and turning into a source of nitrate buildup.
  • Filter Socks and Felt Pads: Positioned to catch debris from the tank overflow, they are effective at polishing the water but require frequent changing or cleaning to maintain efficiency.
  • Protein Skimmers: Though not a mechanical filter in the traditional sense, protein skimmers remove organic compounds directly from the water by creating a foam of microbubbles that organic materials adhere to, which is then collected and removed. This preemptively reduces the load on both mechanical and biological filtration stages.

2. Biological Filtration

Biological filtration is the heart of the nitrogen cycle in an aquarium, converting harmful ammonia and nitrite into less harmful nitrate. This process is facilitated by beneficial bacteria that colonize surfaces within the aquarium. Key components include:

  • Live Rock and Sand: Porous materials that offer vast surfaces for bacterial colonies to establish. They are not only decorative but also functional, serving as an effective natural biological filter.
  • Bio Media: Engineered media designed with high surface area to volume ratios, providing additional space for beneficial bacteria to grow. This media can be housed in a sump, canister filter, or hang-on-back filter, depending on the aquarium setup.

3. Chemical Filtration

Chemical filtration removes dissolved substances from the water through adsorption, absorption, or chemical reaction. This type of filtration can target specific contaminants, including phosphates, silicates, and organic compounds, that biological and mechanical filters can't remove. Common chemical filtration methods include:

  • Activated Carbon: Adsorbs a wide range of organic compounds, improving water clarity and removing odors. However, it needs to be replaced regularly as it becomes saturated.
  • GFO (Granular Ferric Oxide): Effective at removing phosphates, which can contribute to algae growth if left unchecked. Like activated carbon, GFO needs to be replaced periodically.
  • Ion Exchange Resins: These are specialized media designed to remove specific ions from the water, such as nitrates or heavy metals, and can be very effective in targeted applications.

Integration and Maintenance

While each filtration type has its specific function, they are most effective when used in conjunction. Regular maintenance is crucial to keep each system running efficiently. This includes cleaning or replacing mechanical filters to prevent clogs, testing water parameters to ensure biological filtration is effectively managing the nitrogen cycle, and replacing chemical media before its adsorptive capacity is exhausted.

6. Replenish Elements

Maintaining the balance of various elements is crucial for the health and growth of corals. Corals and other invertebrates consume elements such as calcium, magnesium, and alkalinity (carbonate hardness) from the water for their skeletal growth and metabolic processes. As these elements are depleted, they must be replenished to mimic the stable conditions found in natural reef environments. Here’s how you manage this delicate balance through supplementation and monitoring:

Understanding Key Elements

  • Calcium (Ca): Essential for the skeletal structure of corals and coralline algae.
  • Magnesium (Mg): Helps in maintaining the balance of calcium and alkalinity in the water. It’s also crucial for the overall health of the aquarium’s inhabitants.
  • Alkalinity (KH): Represents the water's capacity to maintain pH stability and is vital for the growth and development of corals.
  • Other Elements: Trace elements like iodine, strontium, and potassium also play roles in coral health and coloration but are needed in much smaller quantities.

Testing and Monitoring

Regular testing is fundamental to understand the current levels of these elements in your aquarium water:

  • Test Kits: Use reliable test kits designed for reef aquariums to measure the concentrations of calcium, magnesium, alkalinity, and other significant elements. It’s important to follow the instructions carefully for accurate results.
  • Frequency: Testing frequency can vary based on the tank’s stability and the growth rate of your corals. Weekly testing is common for many aquarists, but more frequent testing may be necessary after dosing adjustments or when adding new corals to the tank.


Based on your test results, you can determine which elements need to be replenished:

  • Balanced Dosing: For many aquarists, using a balanced dosing system that includes calcium, alkalinity, and magnesium in proportionate amounts simplifies maintenance. These are often sold as part of a dosing system or kit.
  • Targeted Supplementation: If individual element levels become unbalanced, you might need to dose them separately to restore harmony. This approach requires careful calculation and adjustment based on the specific needs of your aquarium.
  • Automated Dosing Systems: For consistency and ease, automated dosing pumps can be programmed to add precise amounts of supplements at regular intervals, reducing the likelihood of human error and fluctuations in water chemistry.

Adjustment and Stabilization

  • Gradual Changes: When adjusting levels, it’s critical to make changes gradually to avoid shocking the aquarium’s inhabitants. Sudden shifts in water chemistry can stress or even harm corals and fish.
  • Record Keeping: Keep logs of your test results, dosing amounts, and any changes in the tank’s inhabitants or equipment. This record can help you understand trends over time and make more informed decisions.

Learning and Adapting

  • Research: Different types of corals may have different requirements. Stay informed about the specific needs of your corals and adjust your maintenance routine accordingly.
  • Community Advice: The reef-keeping community is a valuable resource. Don’t hesitate to seek advice from more experienced aquarists or professionals when faced with challenges.

7. Reef Aquarium Placement & Size

Choosing the right reef aquarium involves balancing personal preferences, budget, and the practical aspects of aquarium maintenance. While smaller tanks might seem less demanding in terms of budget, physical effort, and time, they can actually be more challenging to maintain in terms of water chemistry stability. Larger volumes of water tend to fluctuate less rapidly, offering more forgiveness to changes in water parameters. Regardless of size, the location of your reef aquarium within your home or office plays a crucial role in its success and longevity. Here are the key considerations for placing your aquarium:

Avoid Direct Sunlight

  • Temperature Control: Direct sunlight can cause significant fluctuations in tank temperature, potentially stressing or harming the tank's inhabitants.
  • Algae Growth: Sunlight can also accelerate algae growth, leading to maintenance issues and potentially outcompeting corals for nutrients.

Electrical Socket Accessibility

  • Safety and Convenience: Having an electrical socket nearby is essential for powering the tank's lighting, filtration system, heaters, and other equipment. Ensure that the setup complies with safety regulations to prevent electrical hazards.

Floor Support and Leveling

  • Weight Considerations: Aquariums are heavy, especially when filled with water, substrate, rocks, and equipment. Make sure the floor can support the weight of the aquarium to avoid structural damage.
  • Level Surface: An uneven floor can lead to uneven water distribution and pressure on the aquarium, which might stress the seams or even cause leaks. Use a level to ensure the tank is perfectly horizontal during setup.

Proximity to Water Source and Drainage

  • Water Changes and Top-offs: Regular water changes are a part of maintaining a healthy reef aquarium. Easy access to a water source simplifies the process of adding fresh water or preparing saltwater mixtures.
  • Drainage: Being close to a drain makes disposing of old water much easier and less messy, especially for larger volumes.

Additional Considerations

  • Viewing Pleasure: Position the tank where it can be easily viewed and enjoyed without obstructing pathways or essential household functions.
  • Room for Maintenance: Ensure there's enough space around the aquarium to perform regular maintenance tasks comfortably, such as cleaning, testing water parameters, and adding or adjusting equipment.

Planning for Success

The initial setup and location of your reef aquarium can significantly impact its success and your enjoyment. Take the time to consider these factors carefully before installing your tank. Remember, once filled, moving an aquarium is not only difficult but can be risky for both the tank structure and its inhabitants. Proper planning and placement are key steps toward creating a thriving reef ecosystem. 

Review these pages catered to ensure full control and knowledge of you new reef system from us to you:

Saltwater Setup: How Does a Reef Aquarium Work? (current page)

Saltwater Setup: What Equipment will be Needed?

Check out the link to explore the different saltwater options (Saltwater Aquariums).

Tell us how you feel about this post. What would you add? How do you do go about handling these topics yourself? Comments are appreciated.