Water Quality for Reef Tanks (Part 1): The Most Important Parameters

One of the first things that we learn when starting a reef tank is how important it is to keep an eye on our water parameters and to correct them if they get out of range. The best thing for a reef tank is to keep all parameters stable for optimal coral health and growth. A major swing in any one parameter can cause stress and, in many cases, death to coral. This is especially true for the most sensitive sps coral. 

In this post, we’ll go over the ten most important water parameters and why they are important. We’ll also identify the best range(s) for these levels in order to keep your reef healthy and thriving, as well as what can happen if the parameters are not kept within the optimal range(s).

Click on a parameter below to learn more:

Calcium | Alkalinity | Magnesium | pH | Temperature | Salinity | Phosphate | Ammonia | Nitrite | Nitrate


Calcium

Calcium

Why It’s Important: Calcium is essential for growing any coral with a skeletal structure, such as large and small polyp stony corals, as well as clams and coralline algae. In tanks with lots of stony corals and clams, calcium can be rapidly depleted. Therefore, it  needs to regularly replenished. Reef invertebrates, commonly used as clean up crew for reefs, also use calcium to build their exoskeleton. 

Optimal Range / Levels: 400 – 450 ppm

What Happens If Its Not Maintained: If calcium is too low, coral growth will be much slower. Some corals may even recede and become discolored or “brown out”. If calcium levels become too high, alkalinity may drop affecting the buffering capacity of water. If alkalinity falls it can create a snowball effect and pH levels will begin to fluctuate, raising the chance of a full blown tank crash.

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Alkalinity

Alkalinity

Why It’s Important:  Alkalinity is important in a reef tank for many reasons.  Proper levels create stability and prevent ph swings. Alkalinity is also used for coral calcification and skeletal formation. Corals such as small polyp stony coral (sps) and large polyp stony coral (lps) tend to use more alkalinity in an aquarium to build their skeleton. They are much more sensitive to swings and improper levels. Keeping your alkalinity stable will help maintain a proper ph in your aquarium and help improve coral growth and health.

Optimal Range / Levels:  8-12dkh
Keep in mind that an ultra low nutrient system (ULNS) may require an alkalinity at the lower range whereas a system with higher nutrients may need to be at the higher range. If you find that your alkalinity level is off, be sure to raise or lower your alkalinity slowly. The phrase to remember here is “Nothing good happens fast in a reef tank.”

What Happens If Its Not Maintained:  If you fail to maintain a proper and stable alkalinity level you are putting the health of your corals at risk.

  • If your alk is slightly low, you may see a decrease in growth and loss of color.  
  • If your alk is substantially low, you may begin to see coral bleaching or rapid tissue necrosis (rtn) or slow tissue necrosis (stn) on sps coral. Rtn and stn is when the tissue of your sps coral peels away from the coral leaving a bare skeleton.  
  • If your Alkalinity is low, your PH will fluctuate more dramatically.
  • If your alkalinity is too high, it may cause burnt tips on your sps corals.This means that the tissue is unable to keep up with skeletal growth, leaving the tissue thin and causing the tips to be burned by the lighting in your aquarium. 
  • High alkalinity can also cause tissue recession in LPS corals. 

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Magnesium

Magnesium

Why It’s Important: Magnesium is used to prevent precipitation of calcium carbonate, which helps maintain the proper levels of calcium and alkalinity. Magnesium carries two positive charges, just like calcium, and is regularly used by stony corals to build their skeletons.

Optimal Range / Levels: 1250 -1350 ppm

What Happens If Its Not Maintained: If magnesium levels are low, it is difficult to maintain proper levels of both calcium and alkalinity. If calcium carbonate precipitation occurs, a white film may develop on pumps and heaters that could shorten their lifespan.

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Acidity

pH

Why It’s Important: pH determines how acidic the water is. It also helps with coral calcification, allowing corals to pull calcium from the water to build their skeletons.

Optimal Range / Levels: 8.0 – 8.4

What Happens If Its Not Maintained: If pH is not stable, coral growth will suffer and large swings in pH can result in coral death. Also a consistently low or consistently high pH will cause stress on corals and can even lead to coral death.

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Temperature

Temperature

Why It’s Important: Temperatures that are too high (above 81) or too low (below 75)  are often referred to as the “silent killer” in a reef tank. Although neither is good, a reef tank is generally more tolerable of cooler temperatures than hotter ones, as hotter water holds less oxygen than cooler water making it difficult for corals and fish to resporate. A constant temperature in a reef tank is very important and will help reduce stress on your corals, as well as improve coral growth and coloration.

Optimal Range / Levels: 75-78 degrees

75-78 degrees would be ideal for a reef tank. Although an aquarium may be fine in temperatures up to 81 degrees.  

What Happens If It’s Not Maintained:  If the water in your tank becomes too hot, too cold, or if the temperatures fluctuates, corals will become stressed. If the water is cold for a period of time the corals will begin to slow their growth, or even stop growing. They may turn brown or could even become bleached. (Bleaching is when a coral expels their symbiotic algae known as zooxanthellae, which is the algae inside of coral that provide the coral with food from photosynthesis.) If your reef tank water becomes too warm, corals begin to stress. They may begin to expel their zooxanthellae resulting in bleaching. An aquarium becoming too warm can cause irreversible damage in corals. However, if your aquarium becomes too cold your coral may have a better chance at recovering or even adjusting.

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Salinity

Salinity

Why It’s Important: Corals need a certain ratio of salt to water in order to survive. Fish can generally tolerate a lower salinity and are treated in hypo salinity to help treat certain parasites . However, corals need a much more stable salinity to thrive.

Optimal Range / Levels: 32-35 parts per thousand (ppt) / 1.024 – 1.028 sg (specific gravity)

What Happens If Its Not Maintained: Corals cannot tolerate a salinity below 31 ppt / 1.023 sg for a prolonged period of time or they will die. On the high side, a salinity in the 36-37 ppt is range is generally tolerated for a short period of time. However, once the salinity reaches 38 ppt / 1.030 sg or higher, soft corals begin to melt and the flesh of many hard corals begins to peel off their skeletons. Even fluctuations in salinity within the optimal range can cause stress on coral and reduce coral health and color.

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Phosphate

Phosphate

Why It’s Important: A little bit of measurable phosphate is needed for coral growth and to help improve coral color. However high amounts of phosphates will generally result in the growth of nuisance algae. Phosphates in an aquarium are usually the result of the breakdown of fish waste, fish food and other tank additives. They also may sometimes be leached from the rock or substrate inside of the aquarium.

Optimal Range / Levels: 0.02 – 0.05 ppm

What Happens If Its Not Maintained: If not kept under control, phosphates will produce brown algae in the tissue of corals turning them their true bright color to brown and green hair algae throughout the entire tank. High phosphates levels can also restrict coral calcium consumption, stunt coral growth and eventually even cause coral death. It is best to be proactive and try and keep phosphate levels low, before they get out of control, by making regular water changes and running phosphate removing media, like GFO (Granular Ferric Oxide).

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Ammonia

Ammonia

Why It’s Important: Ammonia is the first step in the nitrogen cycle / process in an aquarium and as such should be kept at 0 at all times in a fully cycled aquarium.

Optimal Range / Levels: 0

What Happens If Its Not Maintained: If a reef tank is not properly cycled, then it cannot properly rid itself of ammonia. Ammonia is toxic to all life in a reef tank and will immediately begin damaging the exterior cells on corals resulting in likely death.

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Nitrite

Nitrite

Why It’s Important: Nitrite is the second step in the nitrogen cycle / process of converting ammonia into non-toxic form nitrate.

Optimal Range / Levels: 0

What Happens If Its Not Maintained: Nitrites, like ammonia are toxic to most reef inhabitants. Nitrates can cause damage and even death to corals in an improperly cycled tank.

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Nitrate

Nitrate

Why It’s Important: As fish poop and other waste breaks down in an aquarium, it is broken down from ammonia to nitrite to nitrate. Very low amounts of nitrates are required for coral growth and they may help deepen coral colors.

Optimal Range / Levels: 0.025 ppm- 5ppm

What Happens If Its Not Maintained: High levels of nitrate can cause damage, as well as death, to delicate corals, anemones, and other invertebrates. Nitrates make zooxanthellae grow inside of corals, which can decrease their growth and vitality. Nitrates can also contribute to the growth of undesirable algae.

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Summary

Many parameters factor into the health of a reef tank. Every reef tank is different. Some may tolerate higher or lower levels of certain parameters than others. The success to every reef tank is to begin with the proper cycle and get all parameters in check. Once in check, maintain the proper levels. Stability is key to grow and color up coral. The proper parameters will prevent a reef from stress and allow your reef to thrive.

Have a question about a product or need further assistance with your reef tank? Give us a shout at ATI North America, we’d love to hear from you!

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