Comparing Reef Aquarium Test Kits by Keith MacNeil, a Marine Depot Staff Member

I am going to start this article with a confession: I do not like testing the water parameters in my reef aquarium.

I tend to be one of those “lazy” reefers that doesn’t test his tank and just waits until he notices a problem. Then, when a problem does occur, all of a sudden I run every test I can to see what is causing the problem in my tank.

Are my Calcium and Alkalinity levels out of whack? Are my Magnesium or Strontium levels low? What about my Nitrate or Phosphate levels, have they risen and are they what are causing the issue in my tank? If only I had spent that 10-30 minutes each week running a few tests here and there, I probably would have avoided some of the problems I have experienced in the past. That is something I would like to change with my current tank project.

So when I was presented with the chance to write an article on testing water parameters in a reef tank, I thought this would be the perfect opportunity to try out a bunch of different test kits by different manufacturers, report back on them and hopefully find some test kits that I could start using on a weekly basis to keep problems at bay in my tank. 

The goal of this article is not to bash or praise kit X over kit Y, but more so to compare the test results from different manufactures and let you, the reader, decide which kit is best for you. I am also going to include the approximate time it takes to run each test. Obviously this will vary from person to person, but I think it will give a good basis on how long—on average—a test will take. 

While there are many different parameters that should be tested in your tank, I am going to focus on five in particular: Phosphate, Nitrate, Calcium, Alkalinity (KH) and Magnesium. But before we dive into my test results, let’s quickly go over what parameters should be tested in a reef tank along with acceptable levels and ways of testing those parameters:

  • Temperature: While there are different opinions on what is ideal for a reef tank, most people find running their tanks between 78-82 degrees Fahrenheit is best. There are numerous ways of testing your temperature, from thermometers (digital and liquid) to electronic controllers with temperature probes. I use a controller (Neptune Systems AquaController Jr.) to monitor and control my tank temperatures but I also have a Coralife digital thermometer as a back up.
  • Salinity/specific gravity: In layman’s terms, it is the measure of how much salt is in your water. Salinity is the measure of total salts in a given weight of seawater expressed in parts per thousand (ppt). Specific gravity is used by aquarists to measure the salt content of seawater and is a dimensionless valuei . For a reef aquarium, a specific gravity of 1.025-1.026 (salinity of 34-45 ppt) is generally recommended. Most people will use a hydrometer or refractometer to measure their salt levels, but electronic salinity monitors are also available.
  • pH: The measurement of free hydrogen ions in water measured on a scale from 1.0 (acidic) to 14.0 (alkaline). pH is a contraction that stands for pondus Hydrogenii (weight of hydrogen). For a saltwater tank, we want to have a higher pH, with a level between 8.2-8.4. There are a few different options hobbyists have for reading their pH levels. One of the more common options is a liquid test kit. Most test kits use a color chart to find out the value of the pH. The tester will put a known volume of tank water into a test vial, add a few drops of an indicator solution to the vial and compare the color the water turns to a color chart that will correspond to a pH value on a chart. While an easy test to perform, comparing the colors can be hard especially if you are color blind or in a dark room. I have gone to electronic monitors for reading the pH in my tanks. They use a probe to measure the pH of the aquarium and will give a digital read out of the levels. While they can be quite a bit more money to purchase, they will monitor your pH levels 24/7, are easier to read and the monitor itself should last for a long time (my first pH monitor is still going strong after 14 years). The probes should be changed about every 18 months though.
  • Ammonia/Nitrite: Both of these are toxic, especially in high levels, to the livestock in your tank and should be maintained at undetectable levels (i.e. 0). Nitrite is less toxic in a saltwater aquarium than a freshwater aquarium, but none the less, maintaining the levels at zero is still ideal. With established biological filtration in an aquarium neither should be an issue, but when a tank is first set up, these levels should be monitored weekly or even a few times per week. Once the tank has fully cycled, normally testing their levels sporadically is fine (once a month to every other month). Liquid or dry reagent test kits for ammonia and nitrite are the most affordable and practical way of testing for their levels in our home aquariums. Like the pH test kits, a color chart comparison will be used to find the level of ammonia or nitrite within the aquarium.
  • Nitrate: The final byproduct of the nitrogen cycle (ammonia is broken down by bacteria into nitrite and then into nitrate by a different bacteria). While it is generally not considered harmful to fish, moderate to high levels can cause significant problems with many invertebrates (including death and other health issues) and can also lead to problematic algae growths within a tank. Keeping nitrate levels low (ideally at or very close to zero within a reef tank) is very important to the overall health of the tank and therefore monitoring their levels is very important. While this article won’t go into ways of reducing nitrate levels, you can find more information about that here. The most popular way of monitoring the nitrate levels within a tank is by using a test kit, but there are also electronic monitors available for those who wish to view up-to-the-second nitrate levels within their aquarium.
  • Phosphate: Like nitrates, phosphates are another fuel for algae and can even inhibit the ability of corals to utilize Calcium from the water. Phosphates can be introduced into the aquarium numerous ways, but most commonly are introduced from the food fed to your fish, from tap water or from additives or supplements used. Again, we’re not going to go into ways to reduce phosphates, but I will suggest the use of phosphate removers as one of the best methods. Testing of phosphate levels is most commonly done with a standard test kit (liquid or dry tabs), but there are also Photometers that allow for a more precise and more accurate reading of phosphates even at low levels.
  • Calcium: Calcium is the building block of the calcareous organisms within our reef tank. Corals, clams, coralline algae (and other calcareous algae like halemida), feather dusters and many other organisms rely on Calcium to build their skeletons or skeletal structures. Maintaining a proper Calcium level is very important to all these animals. Calcium also has a strong relationship with Alkalinity levels within the aquarium. According to Mike Paletta in this article, “There is a strong relationship between Calcium levels and Alkalinity that should not be neglected. If the Calcium levels get high (over 500) there is a tendency for Alkalinity to drop. Conversely, if Alkalinity levels get too high, Calcium levels will tend to fall as Calcium precipitates out.” Calcium levels ideally should be kept around 350-450 parts per million (ppm) and there are numerous test kits available for testing the Calcium levels of your tanks water, most using a titration method to determine their levels.
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Starting color for titration (Salifert kit)

Ending color for titration (Salifert kit)

  • Alkalinity: It is the capacity of a system (the water) to resist a downward change in pH and is also known as carbonate hardness. It can be measured with two different readings, milliequivalents per liter (meq/L) or degrees of carbonate hardness (dKH). Some test kits will give readings in one, the other or both. A higher Alkalinity level within the tank can help avoid rapid changes in the pH of system and, as mentioned in the Calcium description, it can have a direct effect on the Calcium levels within the tank. Natural seawater has a value of around 7 dKH (slightly lower in some areas and slightly higher in others). Most people recommend keeping the Alkalinity levels between 8-12 dKH in our home aquariums. Like Calcium test kits, there are numerous test kits available for Alkalinity as well, many using a titration method or simple color change methods to determine the Alkalinity levels.
  • Magnesium: It is the third most abundant ion found in seawater and plays a direct role in helping to maintain Calcium and Alkalinity levels within the aquarium. When Magnesium levels fall too low within the tank it causes Calcium to precipitate out of the water as well as Alkalinity levels to drop. By maintaining Magnesium levels within the tank, it will help keep the Calcium and Alkalinity levels in balance as well. If you are having issues with your Calcium and Alkalinity levels and you haven’t checked you Magnesium, that would be a great starting point. Your Magnesium levels should be around 3 times what your Calcium levels are running at. In natural sea water, the levels are around 1285 ppm, but the levels will be less in areas where the specific gravity is lower. Testing of Magnesium levels are also done with a titration test kit.
  • Strontium: Strontium is similar to Calcium (chemically) and therefore is utilized by corals to help build their skeletons. According to Sprung/Delbeek in their book The Reef Aquarium Vol. 3, “Anecdotal reports by aquarists link Strontium supplementation with rapid coral growth.” In natural sea water the levels of Strontium are found to be around 8 ppm (meq/L). We should try to maintain those levels within our aquarium as well. Titration kits from Seachem and Salifert are available for testing Strontium levels.
  • Iodine: I am not going to get into trying to explain Iodine, Iodate, Iodide, etc. since this can be confusing for many people (including myself). For a good explanation of the various forms of Iodine, check out page 184-185 of The Reef Aquarium Vol. 3. Iodine is found in most soft corals, marine algae, gorgonians and anemones tissue and helps with the growth of these organisms. Many people also use Iodine as a dip for their newly acquired corals as a preventative. Iodine kills bacteria and can help any damaged corals by killing off bacteria that could lead to infections. Test kits are available for testing Iodine levels by manufacturers like Red Sea, Seachem and Salifert. If you are dosing Iodine supplements, it is a very good idea to test their levels to prevent over dosing the tank.
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So, without any further ado, let’s take a look at some test results I gathered over approximately one month’s span with test kits from APISeachem, Tunze, ElosSalifert and Red Sea. All kits were brand new before starting this testing with the exception of a few Salifert test kits that I had purchased years ago. I wanted to throw in the results of the “old” Salifert kits to get a comparison to the new ones I received.

Phosphate Test Kits


Phosphate Expiration Date Time Results Date Time Results Date Time Results
Tunze 1/31/10 12/16/08 ~5:00 0-.25 12/28/08 ~4:00 1/13/09 ~3:30
Red Sea 10/2010 12/16/08 ~6:00 12/28/08 ~5:00 1/13/09 ~5:00 0-0.1
API not given 12/16/08 ~8:00 12/28/08 ~6:30 1/13/09 ~6:00
Salifert 07/2009 12/16/08 ~3:45 12/28/08 ~3:00 1/13/09 ~3:15
Old Salifert 11/2008 12/16/08 ~3:00 12/28/08 ~3:00 1/13/09 ~2:45
Elos 08/2010 12/16/08 ~6:00 12/28/08 ~4:30 1/13/09 ~6:00
Seachem not given 12/16/08 ~3:00 12/28/08 ~2:30 1/13/09 ~2:00


As the testing progressed and I became more familiar with the instructions, the time it took to run each test decreased. Unfortunately (or fortunately, depending on how you look at it) my tank had no detectable phosphates. So while I was able to verify with multiple test kits of these levels, I wasn’t able to compare how their readings were for higher levels of phosphates. Overall I found all the test kits were easy to use and there were no major issues with any of them.

Since I was getting all zero results from my tank (possibly too new of a set up for the build up of phosphates) I got a sample of water from a fellow hobbyist who had a more established tank. The results from his water were a zero reading for the Tunze and API test kits, 0.1 from the Red Sea test kit, .03-.1 from both the new and old Salifert test kit, less than 0.01 from the Elos and between 0 and 0.05 from the Seachem test kit.

Nitrate Test Kits

Nitrates Expiration Date Time Results Date Time Results Date Time Results
Red Sea 8/2010 12/17/08 ~10:00 12/28/08 ~8:30 1/14/09 ~9:00
API not given 12/17/08 ~10:00 12/28/08 ~9:30 1/14/09 ~8:30
Salifert 06/2010 12/17/08 ~6:00 12/28/08 ~5:30 1/14/09 ~5:30
Elos 10/2009 12/17/08 ~8:00 12/28/08 ~7:30 1/14/09 ~8:00
Seachem not given 12/17/08 ~9:00 12/28/08 ~8:30 1/14/09 ~8:00
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Like phosphates, as I became more familiar with the testing procedures, the testing became quicker and easier. Also like phosphates, my tank had zero readings for nitrates. These test kits were all again fairly easy to use but did take a little longer than testing for phosphates.

I had a phosban reactor that I had taken off my tank about a month earlier (I had run carbon in it) that I had forgotten to clean out. I decided to test this water for nitrates since I figured it would have some levels due to the stagnant water within the reactor. I was correct. For the Red Sea and API test kits I got a level of around 5, with the Salifert test kit I got a reading of around 2.5, the Elos kit gave me a reading of right around 10 and the Seachem test kit gave me a reading between 3 and 5.

Calcium Test Kits

Calcium Expiration Date Time Results Date Time Results Date Time Results Date Time Results
Tunze 05/2010 12/18/08 ~13:00 340 12/29/08 ~10:30 340 1/16/09 ~11:00 340 1/20/09 ~10:00 340
Red Sea Pro 02/2011 12/18/08 ~9:00 380 12/29/08 ~8:00 380 1/16/09 ~5:30 400 1/20/09 ~5:30 400
API not given 12/18/08 ~5:00 380 12/29/08 ~4:45 380 1/16/09 ~5:30 400 1/20/09 ~5:00 380
Salifert 12/2012 12/18/08 ~5:00 355 12/29/08 ~4:30 370 1/16/09 ~3:45 370 1/20/09 ~3:45 375
Old Salifert 09/2009 12/18/08 ~4:00 345 12/29/08 ~3:00 360 1/16/09 ~3:00 360 1/20/09 ~3:15 365
Elos 10/2010 12/18/08 ~10:00 350 12/29/08 ~9:30 370 1/16/09 ~9:30 360 1/20/09 ~9:00 360
Seachem not given 12/18/08 ~9:30 325 12/29/08 ~7:00 375 1/16/09 ~6:00 350 1/20/09 ~6:00 350


The Tunze test kit calls for diluting the tank water that is to be tested with RO water. Unfortunately I don’t use RO water (only DI water), so this may have thrown off their results slightly. Overall these test kits seem to be fairly close in range.

Alkalinity Test Kits

Alkalinity Expiration Date Time Results Date Time Results Date Time Results
Tunze 08/2009 12/20/08 ~2:40 7dKH 1/8/09 ~2:30 9dKH 1/20/09 ~2:30 8dKH
Red Sea Pro 01/2011 12/20/08 --- --- 1/8/09 --- --- 1/20/09 --- ---
API not given 12/20/08 ~4:45 9dKH 1/8/09 ~4:00 11dKH 1/20/09 ~3:30 9dKH
Salifert 6/2013 12/20/08 ~3:30 9.6dKH 1/8/09 ~3:20 11.5dKH 1/20/09 ~3:30 10.6dKH
Old Salifert 6/2009 12/20/08 ~2:50 8.6dKH 1/8/09 ~2:45 9.9dKH 1/20/09 ~3:00 9.5dKH
Elos 11/2010 12/20/08 ~4:20 8.5dKH 1/8/09 ~3:45 9.5dKH 1/20/09 ~3:00 9.5dKH
Seachem not given 12/20/08 ~4:00 8.4dKH 1/8/09 ~4:00 11dKH 1/20/09 ~3:40 9.8dKH


All the kits were very easy to use and the results were all fairly close together. I did have problems with the Red Sea Pro test kit though. The ending color was suppose to be purple (color change was from blue to purple). Unfortunately I could never get purple to come up, it would go from Blue to light green to orange so I could not get a result from their kit.

Magnesium Test Kits

Magnesium Expiration Date Time Results Date Time Results Date Time Results
Red Sea 12/2010 12/23/08 ~9:00 1500 1/8/09 ~10:00 1600 1/20/09 ~6:45 1460
Old Salifert 3/2008 12/23/08 ~5:30 1200 1/8/09 ~5:30 1185 1/20/09 ~4:45 1200
Seachem not given 12/23/08 ~14:30 1250 1/8/09 ~12:15 1188 1/20/09 ~12:20 1240


The Salifert test kit and Seachem test kit both seemed to get very similar results and while the Seachem did take more time to run, it was a little more precise in its readings. I once again had problems with the Red Sea test kit in getting an accurate color change. It was suppose to change to blue, but I could only get a purple color to form. I went with the purple color.


Now that I have run a few tests and noted the time it takes to run a test along with results you can judge for yourself which test kit will be best suited for you and your aquarium. Don’t put off testing your water until you see a problem occur in the tank. Be proactive and keep on top of testing and your tank will be better off in the long run. The testing will not only alert you to possible problems, but also aid in the proper dosing of additives and supplements.

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