Other important water parameters

9 Most Important Reef Tank Parameters

The 9 MOST IMPORTANT Reef Tank Parameters are:

  1. Alkalinity
  2. Ammonia
  3. Calcium
  4. Nitrate
  5. Nitrite
  6. pH
  7. Phosphate
  8. Salinity
  9. Temperature

Let’s dive a little deeper into each individual water parameter as well as the value considered to be ideal for a reef tank:

Number 1: Alkalinity

Alkalinity is a complex concept/thing to describe because it pretty much only has scientific explanations. As aquarists, we don’t care so much about the scientific definition of it, as much as we care that because of the chemistry, measuring alkalinity is a way to estimate the amount of bicarbonate that is available in the water, and bicarbonate is a very important molecular compound for the health of our reef tanks.

Why is alkalinity important in a reef tank? Alkalinity impacts the pH of the water (pH is the number 6 most important water parameter). Equally importantly, alkalinity’s role in affecting the available bicarbonate in your tank is important, because bicarbonate is one of the main ‘ingredients’ used to build coral skeletons. You need to keep alkalinity in the appropriate range in a reef tank to ensure there is sufficient bicarbonate for your corals to grow.

Ideal Alkalinity for a Reef Tank

The ideal alkalinity for a reef tank is 8-12 dkh. That’s a pretty broad range. Perhaps more important than reaching a level within that range is to try and stay consistent with that range, once you have found alkalinity level that suits the inhabitants of your tank and is easy to maintain, based on your local water.

Although the accepted range is 8-12 dkh, your aquarium won’t do well if the alkalinity drifts dramatically from day to day. Do what you can to maintain stable alkalinity–and even if you are trying to get your alkalinity up (if it is low, for example), you will want to do so very, very gradually to avoid shocking any of the animals in your system.

Number 2: Ammonia

That same chemical in your glass cleaner that helps make your glass shine and be streak free, is probably also inside your saltwater aquarium and is the number 2 reef tank parameter to watch.

Ammonia occurs naturally, as a byproduct of some sort of organic waste breaking down in your tank. Ammonia gets into your reef tank when your fish…um…pee…and also when food or other stuff rots. From that perspective, it is perfectly natural to have it. The problem is that ammonia is toxic waste in your aquarium. In chemical terms, ammonia is a base, or a basic compound, which sort of means it is the opposite of an acid.

But while acids and bases are kind of like ‘opposites’, they cause a similar type of burning, when they contact living things. The ammonia in your tank will burn your fish and corals and even kill them, if high enough.

water parameter testing for ammonia

Ammonia test kit

The good news is that a  healthy, fully-functioning biological filter protects your tank by removing ammonia from your water. If you have detectable levels of ammonia in your tank, it means your aquarium is too new (has not fully cycled yet) or there is a problem with your biological filter.

Learn more about cycling a fish tank here.

Ideal Ammonia Parameter for a Reef Tank

As another one of the most important reef tank parameters, the ideal ammonia level for a reef aquarium is ~0 ppm. If your tank has fully cycled, there should be no detectable levels of ammonia. Ammonia can burn your fish and corals and at higher levels, it can be toxic.

Number 3: Calcium

Everyone who has seen a milk commercial on television knows that calcium promotes good bone growth. And, well, they don’t drink milk. Now that I think about it, bringing up milk didn’t really help this story much. So, let’s just cut to the chase.

Calcium is an extremely important element in a reef tank and is essential for coral health, because, while they don’t have bones, they do have bony skeletons made from calcium, and they get that calcium from the seawater.

For that reason, calcium is ranked as the third most important of the reef tank aquarium water parameters.

Ideal reef tank parameter for Calcium

Natural coral reefs tend to have calcium levels between 380-420 ppm (parts per million). That’s a fairly narrow range around~400, so, to keep things simple, I generally think of the optimal level to be about 400 ppm.

Number 4 water parameter: Nitrate

The fourth most important water parameter for you to monitor in your reef tank is nitrate. Technically speaking, the presence of low levels of nitrates in your tank could be considered a good thing–because it means that your biological filter is working.

In a properly cycled aquarium, bacteria convert nitrogen waste (often in the form of ammonia) into nitrite and then other bacteria turn that nitrite into nitrate.

The problem is that as your aquarium gets more crowded and mature, it will generate more nitrate and those levels will climb.

Small amounts of nitrogen in the nitrates can be absorbed by certain soft corals or macroalgae, but it can also act as a sort of fertilizer, boosting problem algae growth–which nobody wants.

Some invertebrates are intolerant of high nitrate levels and their health will decline (adding more to the nitrates problem), if left unattended to.

How to reduce nitrates from your reef tank

The fastest, most natural and lowest-tech way to remove nitrates from your reef tank is to perform a partial water change. To help keep your nitrates low on an ongoing basis, some hobbyists employ the help of beneficial bacteria who eat the nitrates.

They accomplish this via a process called carbon dosing. What is carbon dosing, you ask?

The short version, here, is that these beneficial bacteria naturally grow in your tank, but you can give their populations a boost by adding carbon to your tank. Two common ways to do this are through the use of biopellets or vodka dosing.

Spoiler alert, the proper regimen for dosing vodka in the tank is not…one for the tank and one for me.

Ideal reef aquarium value for Nitrate

The ideal reef aquarium value for nitrates is ~0 ppm. However, you may be able to ‘get away with’ slightly higher levels.

On an ongoing basis, you want to strive for nitrate levels as low as possible. However, levels around 30-40 ppm are generally tolerated by most saltwater aquarium fish (except for fragile species) and many hardy soft corals that tend to come from nutrient-rich waters. 

Number 5: Nitrite

The fifth most important saltwater aquarium water parameter is nitrite. No, that is not a typo, nitrite and nitrate are two separate and important compounds to monitor, in your water.

Nitrite is an intermediate by-product produced by your bacterial filter as part of the nitrogen cycle. In your filter, bacteria convert toxic ammonia, as a first step, into less toxic nitrite, before the second group of bacteria converts the nitrite to nitrate.

Ideal Nitrite level for a reef tank

For a very brief period of time (a few days, max), while you are cycling your tank, you will look for the presence of nitrites in your tank, as evidence that naturally occurring, beneficial bacteria have colonized your tank.

Other than that, you want your nitrites to remain as close to zero as possible. If you see any level other than zero, while you’re testing your water, it is a symptom that either your biological filter has crashed, or that it just can’t keep up with some large source of ammonia (like from a dead fish).

That is the reason that nitrite is one of the 5th most important reef tank parameter.

Number 6: pH

I won’t bore you, too much, with the scientific definition of what pH is. It has something to do with hydrogen ions, the scale is logarithmic, meaning that 8.0 is a lot farther from 7.0 than it seems, and apparently, it is very important for some deodorant to be pH balanced for women (or at least that’s what the commercials tell me).

The way I think about pH is this: the pH level tells me how acidic (or not acidic) the water is.

The scale reads from ‘acidic’ on the low end to ‘basic’ on the high end. The pH is essential to how all of the chemistry in your reef tank works, which is why pH is one of the 9 most important reef tank parameters.

Ideal pH for a reef aquarium

The range you want to aim for is: ~8.1-8.4

While the absolute pH is important, it is perhaps even more important to ensure that the pH remains stable. Dramatic swings in pH can cause problems for your livestock.

If your pH either starts or falls out of that range, take your time raising or lowering the water over hours or days (depending on how dramatic the difference is) to avoid shocking your fish, corals and other invertebrates.

Number 7: Phosphate

The seventh most important reef tank water parameter to monitor is phosphate.

Phosphate occurs naturally on reefs and is present at a level of ~0.13 ppm, but it can be a big-time problem-maker in your tank, even at natural levels.

Because in your saltwater aquarium, phosphate acts as a fertilizer for algae, and if your tank is like mine, you probably don’t have the same types of algae-eating controls as a natural reef does.

Ideal phosphate level for a saltwater tank

Determining the ideal level of phosphates for a reef tank is a bit of a tricky subject. Since it fuels problem algae growth, you want to keep it low and may be tempted to keep it at or near zero.

But it is also a nutrient.

Because of that, I recommend you keep levels below 0.2 ppm if possible.<0.2 ppm.

To keep your levels low, you might consider running a phosphate reducing media in a media reactor.

Number 8: Salinity

The eighth most important reef tank water parameter is salinity. When I say that the salinity of the reef tank water is important, what I’m referring to is the amount of salt in the salt water. Get it?

But salinity is relatively difficult to measure directly.

One way you could measure the salinity of the water is to completely evaporate a liter of saltwater and weigh the salt that is left behind. The salt left behind from a liter of saltwater would be your salinity.

Luckily, some super-smart people came up with a few super-easy ways to estimate salinity super-easily.

When the salinity of the water changes, two other important things change:

  • the density of the water changes and
  • the way it bends light changes

So, as hobbyists, we use a hydrometer to measure the density (specific gravity) of the water, or we use a refractometer to measure the angle of light refraction, to estimate the salinity.

Ok, speaking of bending light, I love this band:

You have to have salt in the water to measure salinity. Most of us make our own seawater with a salt mix.

Check out this article to learn about the top reef aquarium salt mixes and which brands are the most popular.

Ideal reef tank salinity level–measured as specific gravity

The salinity of the ocean is actually ~ 35 g/L, but for your saltwater aquarium, it is more common to measure the specific gravity of the water as a proxy for salinity, because of how easily specific gravity can be measured. Ideally, you want to keep your aquarium reef at a specific gravity of  1.025, which is the simplest way to ensure the salinity replicates the salt concentration of a natural reef.

Number 9: Temperature

The ninth most important reef tank water parameter is temperature.

The majority of animals we keep in our tanks come from tropical reefs, and tropical reefs tend to have a stable temperature somewhere between 73 and 84 degrees Fahrenheit, or 22 to 29 degrees Celcius.

If you live in an area where the ambient temperature matches that range…

well, then I’m a bit jealous and hope you’ll invite me over to hang out very soon.

If you don’t live in an area with a steady tropical temperature like that, then you will need equipment to keep the aquarium temperature in the right zone.

An aquarium heater is probably required for just about any aquarium because most of us live in houses where the daily temperature is lower than the ideal values listed below. The aquarium heater raises the water temperature and helps keep it from falling below that level.

If you live in a warm climate, where the temperature gets above the ideal range, you may need an aquarium chiller. Check out this article for reviews to find the best aquarium chiller for your aquarium.

Ideal Value

Since most of what we do is intended to recreate the natural environment our animal friends have come from, it should be no surprise to you that the ideal recommended temperature for your reef tank is the same. The recommended range is:

73-84 Fahrenheit or 22-29 Celcius

That’s a pretty broad range–and you might experience some challenges with finicky species at the extremes. Within that acceptable range, the most commonly provided advice tends to be to keep your aquarium temperature around 78-80 degrees Fahrenheit or 25.5-26.6 degrees Celcius.

As long as the temperature of your saltwater aquarium is in this range, keeping the temperature consistent (avoiding fluctuation) becomes more important than the actual value itself.

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