Water Parameters and Aquariums Part 1

Water quality and the importance of it are some of the things that are commonly talked about when keeping saltwater and freshwater aquariums. With more complex systems there are more factors that come into play and should be focused on or looked at. This article will go over some of the most common water quality parameters for both FOWLR tanks and reef tanks. The following parameters - temperature, Salinity, pH, nitrate, nitrite, and ammonia-  are parameters which are considered to be basic and are almost always in the lineup when water testing is done no matter the type of tank. Other parameters such as alkalinity, calcium, magnesium, and phosphate are parameters that need to be considered for testing, especially if the system is a reef tank, and those will be covered in a second article of this series.


There are several important water parameters that come into play when keeping an aquarium. No matter if the tank is going to be salt, fresh, or even a brackish tank, the temperature that a tank is kept at is incredibly important. The species of fish, coral, or plants that are being kept in the tank will determine the temperature. On average most saltwater tanks have a temperature range from 78-81 degrees Fahrenheit (25.5-27 C). There are certain species of fish and corals that prefer slightly warmer temperatures, and there are also species that will only thrive in cooler temperatures like those that are associated with deeper waters. Temperature is an important factor to consider when performing water changes or topping tanks off, especially in the winter and summer months. The temperature of the new water that is being added should be matched to the temperature of the existing tank water.

Swings in temperature can create unnecessary stress for the fish and coral, so it is best to keep it stable. While it might not seem that way, most fish and coral can handle small, gradual changes in water parameters. With respect to temperature, generally they will be able to handle cold better than they can handle excessive heat. If a swing does happen, try to slowly adjust the temperature to reduce creating more unnecessary shock for them.   

 When measuring temperature, there are a variety of options from the stick on temperature strips, to glass thermometers, and digital sensors. The stickers are okay, but are not the most accurate and break down over time. Just as affordable though,  are the floating thermometers and they are always accurate. On the higher end of the spectrum are the digital temperature probes which are accurate, provided they are kept calibrated. Many high end heaters have temperature probes on them so this is another option.


When it comes to keeping saltwater fish tanks, after pH, salinity is arguably one of the most important water quality parameters.  Salinity is a measure of the amount of salt that is dissolved into a given amount of water. Salinity can be measured in 2 different ways PPT (parts per thousand) which is read 35ppt, or as specific gravity, which is read 1.026.  Saltwater reef aquariums typically have salinities that are 1.026 or 35ppt, however those values are flexible. When it comes to fish only tanks and tanks with soft corals, the salinity can range from 1.020 all the way up to 1.026.

Quarantine tanks and tanks to treat fish who are sick can have salinities that are significantly further below 1.020. The reason to keep salinity so low when it comes to quarantine and sick fish, is due to the fact that fish can handle the lower salinities while the parasites cannot. Like with other parameters fish and coral can handle changes. With respect to fish, they can handle rapid drops in salinity, however the it should be increased slowly to return them to a higher target salinity. Corals on the other hand are less tolerant of large swings either way. Oftentimes wholesalers will keep salinities lower for their fish, which is why it is important to test the water and slowly acclimate new fish and coral and not just place them directly in the tank.

When measuring salinity there are a few tools that can be used- refractometers, hydrometers, and digital salinometers. The digital tools like the one from Milwaukee Instruments and Hanna Checker will be the most accurate but they are also the most expensive. The refractometers are a slightly more affordable option and are accurate if they are kept calibrated. The last tool, the hydrometer is the cheapest option, but they are not nearly as accurate as the others. If you are keeping a saltwater aquarium, do yourself a favor and invest in a refractometer.


At some stage in their life, all aquariums have ammonia. It is a necessary part of their initial cycle, but after that it shouldn’t be showing up on test results. While ammonia (NH3 and NH4+) is naturally occurring in any tank, thanks to the waste fish and other organisms produce, there are bacteria that will break the ammonia down into nitrites and nitrates which are easily removed from the system. Ammonia in a tank is toxic; it can and will kill your fish and other invertebrates, so if a test shows a value over 0, it is time for a water change. The pH and temperature of the water can impact the toxicity of the ammonia as it is less toxic at lower temperatures and pH values. If a tank is fully cycled and has ammonia, it is important to determine the source and eliminate it. Sources can include, but are not limited to: dead fish, crabs, snails, excess food that has gone to waste, and other forms of organics.

Ammonia is one of the number one things that is tested on every tank both freshwater and saltwater and the tests for it are fairly common. They range in complexity and cost from alert strips that suction to the glass and require no effort, to digital test kits. Starting with the most basic, are little plastic sheets that can be stuck or suctioned to the inside of the tank. These are inexpensive and not very accurate as well as being somewhat hard to read. The next way to measure ammonia is to use a dip strip, these are quick and easy and will give you an estimate of the ammonia levels. There are several variations of these on the market from 6-in-1 dip strips that include several parameters, to the individual ammonia tests. Slightly more complex are the test kits where a sample of the tank water is mixed with reagents and let sit for a period of time. The color of the liquid in the vial will be compared to a color sheet to determine the concentration of ammonia. These kits can range in cost depending on the brand. The last type of ammonia test is by using a digital test kit. These are significantly more reliable and more accurate.


Another water parameter that should always be tested in both freshwater and saltwater tanks is pH. In simple terms, pH is a measure of acidity. The pH of freshwater is 7 and is considered neutral. When keeping aquariums, the average pH can differ between freshwater and saltwater tanks. Saltwater and reef tanks have a target pH of 8.4, though it can range from 8.0-8.4. Freshwater fish, depending on the species, can live in a much larger pH range. Fish cannot tolerate dramatic swings in pH which is one of the many reasons it is critical to acclimate them. An additional factor to be mindful of is that pH has a relationship with things like temperature, ammonia, and alkalinity.

Like with the parameters listed above, there are a variety of different methods that can be used to test for pH. There are the dip strip tests, test kits, digital tests, and even pH monitoring that is tied into aquarium controllers. Like with the ammonia dip strips they are available as individual test strips, as well as in multi parameter tests. Likewise, the test kits range in cost, and the pH is measured by comparing the color of the water sample (with added chemicals or reagents) to a color chart. Lastly, and with the highest cost are the digital tests. These can range from the handheld Hanna Checkers to the Felix Smart, Hydros, and Apex aquarium controllers that regularly monitor pH (when the appropriate probes are installed) and send results to an app on your phone. For the average new aquarist, it might be best to stick with the test kits. They are easy to use, accurate and affordable.


Out of all the basic tests run on an aquarium, a nitrate test is likely to be the only one where it is not immediately life threatening if the values are over the target amount. Ammonia is broken down by bacteria into nitrites, which are then broken down into nitrates. The target range for nitrates depends on if a tank is a reef tank or a FOWLR tank. In FOWLR (Fish Only With Live Rock) tanks it is acceptable for the nitrates to be between 0 and 40ppm, but when it comes to reef tanks, the target nitrate range is much lower- .25 to 5 ppm. Nitrate values can creep up quickly, but they can also be fixed easily through water changes.

Nitrate isn’t as deadly to fish and corals as nitrites and ammonia, but it should still be kept at an appropriate level. Oftentimes elevated nitrates are also tied to elevated phosphates and unsightly algae blooms. Nitrate levels are easy to monitor with a quick test. Dip strips or the all-in-one strips won't give you the precise value of your nitrate, they will still work and give you a good estimate. Oftentimes those estimates are enough to let you know if it is time to do a water change or if your levels are still in their target range. Other options for testing include the test kits where the color of a mixture of chemicals and sample water is compared to a color chart with a given value. As with the parameters listed above, there are high end digital test kits which are also available. Despite their extra cost, they are much more precise and if you have a reef tank with specialty or sensitive corals these might be the best way to go.


Not to be confused with nitrate, nitrite is the first step in the process of ammonia being broken down by nitrifying bacteria. Nitrite can be nearly as toxic for fish as ammonia. Any nitrite value other than 0 should result in a water change. If a tank is well taken care of the only time nitrite should be present is during the initial start up stages when the tank is first cycling. To reduce the risk of the nitrites spiking, try to add species to the tank slowly and over time versus stocking the tank all at once.

The tests for nitrite are similar to the tests that are done for nitrate. On the more complex end of the spectrum are the digital test kits which give a more exact value. However, a more cost effective test, which provides accurate results, are the test kits where chemical reagents are mixed with a water sample from the tank to produce a color reaction. This color is then compared with a chart and a value for nitrite is given. The last type of test for nitrites are the dip strips, which aren’t nearly as reliable. Especially in the beginning, when a tank is being newly set up, test kits that provide slightly more accurate results are recommended.

Nitrite, nitrate, ammonia, pH, temperature, and salinity are the most common and basic water parameters tested in saltwater aquariums. There are several more parameters such as alkalinity, calcium, magnesium, and phosphate which are also important to monitor when it comes to keeping a saltwater reef tank. Those parameters will be discussed in part 2 of this series and should not be missed.


Hilary Jaffe