10 Most Important Water Parameters For A Reef Tank

In this article, you will learn the 10 most important water parameters for a reef tank.

Having a reef tank can add so much vibrant color, tranquility, and beauty to any home or business. Maintaining certain kinds of aquariums isn’t always an easy task though, and this especially goes for a reef tank. There many different water parameters to keep an eye on if you want to maintain a healthy reef tank.

So I have compiled this list of specific water parameters for you to test and monitor in your reef tank.

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



water levels for saltwater tanks

1. Alkalinity


The first parameter is the alkalinity. In layman’s terms, measuring the alkalinity not only impacts the PH levels of your water, but it is also a way to estimate the amount of bicarbonate that is available in the water.

Bicarbonate is a really important aspect of maintaining a healthy tank. It is one of the main components used to build coral skeletons. So, it’s vital that you maintain a healthy alkaline level in your water so that your bicarbonate level will also be good, and your coral can thrive.

The ideal alkalinity level for a reef tank is between 8-12 dKH or 142 to 215 ppm.

My latest alkalinity check using the Hanna tester showed 176 ppm.



If your alkaline levels don’t rest here, then your tank is not going to do well. 8-12 might not seem like it is a broad range, but it is. You must find an alkalinity level that suits the aquatic life in your tank and then do whatever you can to maintain those levels.

If your alkalinity is at a 9, for example, keep it at 9. And if you must change it to accommodate the aquatic life in your tank, then do it very gradually.

It can’t jump from one level to another because it can shock your fish, make them ill, and cause havoc in your whole tank. So, get it at a healthy level and try to maintain it there, at that level.

Consistency is a wonderful thing when it comes to alkaline levels. You can change the alkaline levels by doing a water change (slowly and gradually), you can add rocks or substrate, you can even add peat moss. A reverse osmosis filter can also be very useful in maintaining a good PH balance.

This is a great RODI filter system that is affordable and works great. You can get it on Amazon by clicking the link.

If you want to learn more about using RODI water in your saltwater tank, read the article here.

You can test your water’s alkaline levels with an alkaline testing kit. There are many different testing kits available.

I recommend the Hanna Alkalinity tester.  The link will take you to my full review of this tester.

How To Change The Alkalinity levels In A Saltwater Tank


Pro Tip: You will often hear me say that water changes are the answer to many problems encountered in a saltwater tank. While not always the case, most things can be addressed by simply performing a water change on your tank. So for the rest of the items in this list, if you want to maintain or make a change to a certain water parameter, do a water change!


2. Ammonia


Ammonia occurs naturally in every tank. It is a byproduct of waste and it can even occur if food is left in the tank and it begins to rot.

There isn’t much you can do about ammonia, to be honest. Unless you have specially trained fish that know how to hop out of the tank and use the restroom like a human, there are going to be small levels of ammonia in your tank.

Ammonia is one of those items that can be difficult to test for. Most hobby grade testers may show ammonia levels at 0 when there will always be a small trace of it providing you are keeping up with good husbandry.

The issue with ammonia is that it can burn and even kill your aquarium life if the levels get out of hand. Use a good quality testing kit to measure the ammonia levels in your tank. You need to ensure that you have plenty of healthy, biological filtration to keep the ammonia away.

For saltwater tank owners, having a good amount of live rock, and a healthy sump system will help. If you have a healthy, cycled aquarium, you shouldn’t have an issue with ammonia. A healthy ammonia level is 0ppm. A good biological filter will help clean all of that ammonia up and keep your tank nice and healthy.

A good test kit to check for ammonia is the Red Sea Marine Care kit.


3. Calcium


Calcium is vital in a reef tank because the coral needs it to stay healthy and thrive. Although coral doesn’t exactly have bones, their skeletons are made up of calcium.

Natural coral reefs tend to have calcium levels between 380-420 ppm. The optimal level for a tank should be around 400.

Not only do corals require it, but Coraline algae needs a constant supply of it as well.

As the calcium levels are used up and depleted in your tank, it must be replenished in order to keep levels at the optimum.

Some methods used to supplement calcium in your reef tank include:

  • Kalkwasser (Calcium hydroxide)
  • Calcium chloride and buffer
  • Liquid or dry supplements
  • Calcium reactor

Once again, you can buy a tester to see the calcium levels in your tank. I recommend Hanna Calcium tester. It will give you the most accurate reading.

You don’t want to go too overboard with it because too much calcium could make your fish ill. On the other hand, going without it will kill your coral and then your fish will sure to follow. Reef tanks need their coral to thrive so maintaining a healthy calcium level is important.



4. Nitrate


We always strive to have low nitrate levels in our tank. Low nitrates mean that your biological filter is working well. In a properly cycled aquarium, nitrates shouldn’t be a problem.

Nitrate is the final by-product of fish waste and the cycling process of an aquarium.

But if you do have high levels of nitrate, this can accelerate the growth of nuisance algae, which can be toxic to your fish in large doses. Other problems of high nitrate include:

  • Reduced coral health
  • Fish and Invertebrate death

Much like ammonia, you’re never going to be completely rid of it. Small amounts of nitrate are completely normal and unavoidable.

You can control the nitrate level in your saltwater tank by doing the following:

  • Water changes
  • Reduce bioload
  • Reduce feedings
  • Liquid nitrate remover
  • Use a biopellet reactor
  • Use a refugium
  • Use a nitrate reactor

You can use a nitrate tester to check these levels and if you discover that they are a little higher than you’d like, you can control it by using the methods mentioned above. Also consider carbon dosing if you are having a difficult time keeping the nitrate level low.

To check your nitrate level, I recommend the Salifert testing kit.


5. Nitrite


Nitrite is another issue and you definitely don’t want it in your tank. Not to be confused with nitrate, just mentioned above.

Nitrites are a form of dissolved nitrogen that occur naturally in the water column. It’s a part of the nitrogen cycle that occurs prior to the creation of nitrates.


Saltwater nitrogen cycle


Ammonia needs to be present in the tank to get nitrites. As fish waste breaks down, it gives off ammonia. This ammonia will break down due to a bacteria forming into nitrite. This is called nitrification.

So nitrites won’t exist without ammonia being present.

Any level of nitrite in your tank is bad. You want this level to be zero. Any amount in your tank can be toxic to livestock and cause death and significant health problems to corals.

If you detect high levels of nitrite in your tank, you should try the following items to lower the level to 0.

  • Water change
  • Add cycled filters
  • Use a water conditioner like Prime

Testing for nitrate can be done by using the Hanna Nitrite tester.

6. PH


Now let’s discuss PH. Explaining PH requires quite a complex, scientific explanation that would be oodles of pages long. So, to spare you a very long read, I’ll tell you the short, easy, version. PH is more or less the amount of acidity in the water. It tells you how acidic or alkaline you tank water is.

The levels of PH must remain stable in your reef tank. Dramatic swings in your tank’s PH level can be bad news for your livestock.

You want your PH level to be between 8.1-8.4.

If your PH levels are too low or too high, you should perform a water change. There are PH buffers available, but for the most part, performing a water change will keep PH levels in check.

Using this Hanna PH tester will give you an accurate reading of your tank’s PH level.

7. Phosphate


Phosphate is an element that occurs naturally in reefs. Every reef tank will be different but you should always have a small amount of phosphate present in your tank. I recommend you keep your tank phosphate level between 0.02 and 0.05 ppm. Even reef tanks with phosphate levels up to 0.10 ppm can be successful.

You want it to stay right there, at that level. Phosphate can act as a natural fertilizer for things like algae.

If algae grow in abundance inside of your tank, it can kill your fish and ruin your whole tank. You don’t want to eliminate it, though. Don’t get rid of the phosphate completely because it is a nutrient. It can be good for coral and even some of the fish that you may have in your tank.

You simply want to keep it at a low level, to prevent any unwanted tank algae growth. Many people keep macroalgae in a refugium to balance out your phosphate levels.

Consider setting up a refugium with chaetomorpha if you notice the phosphate levels get too high.

You can lower phosphate levels by using these methods:

  • Use a protein skimmer
  • Add a refugium with macrolagae
  • Use an algae turf scrubber
  • Use a GFO media reactor
  • Use phosphate removal media
  • Biopellet reactor

Of course testing for phosphate levels is very important. I recommend the Hanna Phosphate tester as it will give you a precise reading.


8. Salinity


The salinity is another really important aspect of a healthy reef tank. The salinity is the amount of salt in your tank’s water. You want the salt to mimic the ocean’s salt levels.

A good salinity level is around 32-33 ppt. It should have a gravity level of 1.024-1.025. You should test this using a quality refractometer.

If you notice the salinity is too high, perform a water change and replace with RODI water to bring the salt level down.

If the salinity is too low, again perform a water change with RODI water that is pre-mixed to the right salinity level.

The refractometer that I recommend is the Red Sea on Amazon. 


refractometer for reef tanks

9. Temperature


Temperature is another important water parameter to keep in check. Most reefs have temperatures around 73-84 degrees Fahrenheit and you should aim to keep your tank water the same. A smaller range to aim for is between 75-79F. Most livestock fits in this range. I have been keeping my saltwater tanks at 79F for many years.

So, unless you live somewhere where it stays this warm and tropical, you’re going to need a heater to keep your tank at a healthy temperature.

If you live in a place where it gets really hot, then you might want to consider getting an aquarium chiller.

This can help to balance the heat and keep it at bay so that your tank water won’t get too warm.

Keeping the water temperature constant is important. You can avoid temperature fluctuations by using a controller. These are not expensive and you can save yourself from a disaster by using one. Trust me I know. Read about my temperature mistake here.

Using a properly sized heater for your tank is also necessary to maintain the right temperature.

A general rule of thumb for water volume and heater size:

  • 5-10 gallons – 25-75 watt
  • 15-30 gallons – 50-150 watt
  • 40-50 gallons – 100-300 watt
  • 55-75 gallons – 200-400 watt
  • 75+ gallons – 300-400 watt +

My recommended heater is the Eheim Jager. It is very reliable, durable, and affordable.

Also using the Inkbird temperature controller will prevent your heater from malfunctioning which can destroy a reef tank.

10. Magnesium


Last on our list is Magnesium. It’s very important to keep your magnesium levels between 1250 and 1350 ppm. Magnesium plays a vital role in maintaining coral health. If these levels are too low or too high, your corals will suffer.

Most times, magnesium can be replenished into your tank when you perform water changes. Quality salt mixes will contain a certain level of magnesium. Not all salts are the same and not all reef tanks are the same, so it’s important to test this on a regular basis.

Reef salts will generally have more magnesium than regular salt mixes.


saltwater nutrient comparison



Also, certain corals will have different demands for magnesium. SPS corals are more demanding than LPS corals.

Testing for magnesium can be done using the Red Sea Pro Magnesium test kit.

There are other water parameters that you can test for when keeping a saltwater reef tank. These are 10 of the most common ones to test.

As long as you’ve got these levels under control, you should have a healthy and thriving reef tank!