RSS The importance of testing reef aquarium water

MASA Admin

8 May 2007
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During the first semester in my biochemistry class the professor started the class by bringing out two clear beakers into which he appeared to pour two identical clear fluids. Once they were full, he pulled out a worm and placed it in the first beaker , which it immediately crawled out of. He then took the worm and placed it in the second beaker.

To our astonishment, within seconds the worm started to dissolve. He then pronounced that the first beaker contained pure water and the second pure alcohol. He then asked” does anyone know what this means?’ The quarterback of our football team sitting next to me shouted out “yeah if you drink alcohol you won’t get worms”. “No”, the professor yelled while glaring at him. “You can’t tell what a fluid is simply by looking at it.”

You can’t tell what a fluid is simply by looking at it

Sadly, a lot of us, myself included, often think we know what is in our water simply by looking at it. I have been contacted many times by hobbyists asking why a coral died, or why all of their recently added new corals died, while their old corals were doing great, or why they all of a sudden had an algae bloom, etc. When I ask what their water parameters are, they invariably reply either they were perfect or they don’t know.


Like maintenance, quarantining animals and cleaning the glass, water testing is an unglamorous task that nonetheless is one of the most crucial aspects for having long-term success in the hobby. I don’t care how good your lights are, or how efficient your skimmer is or how much you paid for a frag, none of that matters if you don’t have good consistent water quality and you can’t tell just by looking at the tank how good your water quality is.

As I said, testing the levels of all of the important parameters is probably one of the least fun aspects of keeping a tank and does require some time to do it right. And to be honest most test kits only really give you a close ballpark value for what your tank’s parameters are. I have found and read that there is variability in the measurements between test kits from different companies and sometimes even between kits from the same company.


The author’s soft coral tank doesn’t require quite the level of testing as does a sps dominated tank

Also there can be variability from when a kit is new to when it gets old, that is why the better kits now have an expiration date on them, as it is recognized that reagents, especially liquid ones, can deteriorate over time and thus give false readings. Before I became obsessive about testing my water, I now test the alkalinity in my tanks every day, the alkalinity test kit I was using was over 3 years old.

liquid reagents can deteriorate over time

I knew it was old, but thought to myself, how much could things deteriorate? Since I was biased to think that my water was good and most of the corals looked ok, I assumed that the measurements were spot on and thought this until I started consistently losing corals one by one. Not seeing a problem with my test kit, I brought my tank’s water to a shop to have them test it. Initially all of the measurements came back good, until they got to alkalinity.

The alkalinity in my tank was off the charts at 17, the old alkalinity test kit I had been using was off by that much and not many corals can tolerate this high of a level for very long. Needless to say, this wake-up call kickstarted me to test the water more frequently. So now I test alkalinity daily, calcium, magnesium, salinity and phosphate weekly.


A good quality refractometer, and proper, regular calibration is paramount for managing salinity in a saltwater aquarium

Potassium, strontium, and nitrate are tested once a month, as they are not only not as critical as the other parameters in my opinion, but they also fluctuate less over the short-term. I also check the other parameters daily on the monitor including pH, temperature and ORP. [Ed. Note: Salinity is the most important parameter in keeping a saltwater tank; it is a measurement total for all the dissolved solids in your aquarium and the smaller the tank volume, the more often you should test for it.]

All of the values obtained are kept in a log. Initially they were kept on an Excel spreadsheet on my computer, but I found it took longer to log them in than it did to do the test, so now they are just written down on a log, that sits beside the tank that allows for easy viewing.But if you want to do them on a spreadsheet this will allow you to graph the values over time.


It is important to use a test kit with very clear changes in color

As I have noted I am a big fan of making things easy as that way I am more likely to do the task. For similar reasons I use Elos tests for most of my tests now, as I like that when the color changes it is robust. My eyes are not as good as they used to be and in some of the test kits I have used the color change is too subtle.

I prefer to be able to tell when it has changed easily and I know that the Elos tests are both accurate and consistent. Also Elos is coming out with a colorimeter which will take the guess work out of telling when the color has changed even more. I also do keep Salifert kits around for alkalinity, calcium and magnesium, for when the test results differ markedly from what I expect as a kind of back up.


Elos colorimeter will one day ‘measure’ color changes of water tests

Despite how little I like to do testing I have found several things make it easier and the results more reliable. First, the more often I do a test the quicker I can do it. For the tests I only do once a month, I still need to read the directions every time so this often doubles the time it takes to do the test. For the tests I do often, I can now do the tests without reading the directions, so obviously they get done faster. I also do the tests the same time every time I do them.

Every day at the same time, I check alkalinity and every Saturday at the same time I do all the other tests. In this way the conditions in the tank are approximately the same so if something is out of whack it is more likely to be detected since the test is done consistently at the same time. I also do each of the tests twice. I know most of us only do a second test when the readings are off from what we expect, and sometimes we even do them until we get a reading we want. But due to user error the tests are just as likely to be off and look correct as off and be incorrect. So to make sure I am not missing something, I now do each test twice when I do them.

More than 9 times out of 10 the readings are consistent, but every now and then they differ markedly. When this occurs I run a third test and then try to determine why the tests differed.I have found that there are a lot of ways to introduce user error when doing these tests. It can be as simple as using the top of the meniscus for one test and the bottom for the next or adding the drops differently, so now I try to be consistent in how I do all of these things both within tests and between tests and since I do them often my consistency has improved as well.


A fish only tank like this does not require quite the level of testing nor water with as high a quality as does a reef tank

I know I sound obsessive about testing, and actually it is worse than that as I now not only test the water in all of my tanks daily and weekly, I have five saltwater tanks, but the water for water changes is also tested before it is added as is added to the tank. Also the water from any vendor from whom I have gotten corals is also tested before I add the coral to my tank.

I test the make-up water because I want to make sure it is consistent from batch to batch. At times in the past I have some times seen my tank look worse after a water change than the same or better and initially I could not figure out why. Then I started testing it to determine if it was markedly different from my tank’s water. For the most part most freshly made up synthetic saltwater is consistent from batch to batch, and mine is made up a week before it is used for a water change.

However some salt mixes differ markedly from the water in my tank. I use Instant Ocean for my make-up water mainly because I have been using it for 30 years and it is consistent from batch to batch. But I also know that it is consistently low in magnesium, but I now know by how much so when I mix it up, I just add the same amount of magnesium to each batch and it is good.


Without testing and logging the parameters it is difficult to assess why this purple monster starting receding after 2 years of consistent growth

The reason that I test the water in the bags from newly acquired corals is that as with salt mixes I have found that the water in my tanks can be significantly different from the salt in other’s tanks. In this way if a coral I get does not do well I at least have a starting point as to why. It also gives me an idea of how long and what I need to do to acclimate the new coral to my tank. That is if the water from another tank that a coral has come from is markedly different I may take two or three days to acclimate it the conditions in my tank.

I have found that by acclimating corals where the water it came from is significantly different from mine that doing a gradual acclimation greatly increases the likelihood of its long term survival. And considering what we are paying for frags and how much we hate to lose any coral, I think that knowing the differences and acclimating accordingly is the least we can do to enhance the likelihood of a successful acquisition.


Lots of fish are also not a problem when adequate testing is done

In addition to all of the tests I talked about above I also do one other test every week. Before I start my weekly ritual I take out my ampmeter and test for stray voltage. This may seem like a strange test to run with all of the water tests but by doing so I have twice kept from being shocked or worse as by doing this I found that a heater had cracked and that the wire leading to a powerhead was coming off. I have been shocked and near electrocuted enough that doing this test for 30 seconds each week is now something I feel smart for doing.

Water testing is not rocket science and doing it for the most part does not require a degree in chemistry. But doing it regularly and keeping a log of your results will go a long way in helping you have long term success in the hobby.As I learned in my biochemistry class and in my own tanks the hard way, you can’t tell what’s in the water without testing it. And for the quarterback in my class, he flunked out of the class, but now runs a successful construction company.


Vivid colors like these only occur when the water quality is good, but it is not necessary to chase perfect numbers as these corals are growing well in a tank that registers some nitrate and phosphate

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