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The Perfect Aquarium: Applying the Scientific Method to Your Fish Keeping.

Updated: Nov 14, 2021

Individual human beings have been practicing the scientific method for hundreds of thousands of years. As individuals, we are born into this world with an insatiable curiosity. We observe our surroundings, form theories based on those observations, test those theories and then analyze the results. This is the scientific method. For example, as a child you observe the flame flickering up around the gas range in your mom's kitchen. You wonder what that light is and whether it would move if you touched it. You then proceed to test that theory by touching the flame then quickly withdrawing with some pain. You determine fire is hot and should be avoided in the future. The scientific method is not knew to us. It's how we conduct ourselves on a daily bases for our whole lives.

Humanity as a whole, however, has only been practicing the scientific method since we recognized its potential to standardize the accumulation of knowledge and started systematically writing things down sometime in the 16th century. Since then, the sciences have come a long way in getting us as close as we can to a more accurate picture of how our world works. While science will never be perfect, we get better every day, and closer all the time.

Given what the scientific method is capable of, why on earth would we not apply it to the aquarium hobby? The truth is most of us already have. Just by being humans, we observe, theorize, test and analyze our aquariums all the time. What takes us to the next level, what will bring your aquarium closer to its full potential is systematically tracking and recording your already natural predilections for the scientific method; just like we started doing in the 16th century. Imagine where your aquarium could be with the powerhouse of the scientific method driving it forward.


The first step is to take note of the goings on within your aquarium. This comes naturally as you notice discrepancies or differences in your aquarium as time passes. For example, why is that algae growing faster, why is that coral shrinking, why does that fish hide all the time? Literally any question you ask yourself about your aquarium came from an observation you made.

I wrote in the first step, "to take note". This is the most important part of the scientific method. None of these steps mean anything if you don't record your questions, theories, observations, and conclusions. Recording every step of the process ensures accuracy and precision when you put your theories to the test.

As we go through the steps let's use excess algae growth as our example. So, you have observed excess algae growth and asked the question, "Why is this algae growing faster than before?


Now that you have a question to answer, its time to formulate a theory or two. Write down all the possible reasons you know of why algae could be growing faster. Be sure to utilize all your trusted resources.

  • Nitrates are too high

  • Light is on too long

  • Phosphates are too high

  • Flow is too low

  • Ammonia is too high

Next, it is time to formulate a hypotheses for each theory. Each theory should be broken down into two hypotheses. The first is your alternate hypothesis. Think of this as your positive hypothesis. "If algae is growing too fast, then the nitrates are too high." The second is your null hypothesis. Think of this as your negative hypothesis. "Even though algae is growing too fast, the nitrates were not too high."

We are trying to figure out which hypothesis is true. The positive one that states nitrates are elevated, or the negative one that states nitrates were not elevated.

The second theory's two hypotheses would state; "if the algae is growing too fast, then the light is on too long". Or the negative hypothesis would be; "even though the algae is growing too fast, the light is not on too long." Repeat this process for all your theories.


Now its time to test our hypotheses and determine what the probable cause is for the excess algae growth. Test each theory, one after the other. Do not test them simultaneously or you won't know which variable it was that caused the problem.

Starting with your first theory, determining if nitrates are the cause, measure your nitrate levels. If you have a saltwater tank and they read above 10ppm, or a freshwater tank and they read above 20ppm, you can mark nitrates as a possible cause.

Next, test the phosphates. Any reading above .05 ppm in saltwater and 1ppm in freshwater can be marked as a possible cause.

Now test the ammonia, elevated ammonia levels in newer tanks can cause diatoms (brown algae) to bloom. Anything above .25ppm might be a possible cause.

Then, test the lighting, The only way to do this is to reduce the time the light is on and wait for a visual reduction in algae. This can take quite a while and if its your nutrient levels and not the light then your algae will continue to grow.

Finally, do the same by increasing the flow and wait to see if algae growth responds. Increased flow can limit the ability of cyanobacteria (blue/green algae) to attach and grow.

If you have determined the light or flow to not be the cause, continue testing your nutrient theories by lowering your ammonia, then nitrates, then phosphates. If you can do this one at a time, you'll be able to tell which nutrient it was that was causing the problem. This will also prevent you from purchasing three different types of chemical filter media if you only need one.

On the other hand, the cause of your excess algae could have been all of the above. If this is the case, you will have determined the cause and removed it the same as if you had tested all theories simultaneously, it just took a little longer.


If you don't have the time, or the bloom is particularly bad, its okay to move quickly and tackle all possible causes simultaneously; you'll just miss out on some of the data and knowing exactly what the cause was. If you can pinpoint the exact cause this can help you take steps toward prevention. If you lower your light and all your nutrients at the same time and it works, great, but now you don't know if you can turn your light back up, or whether or not you need to do water changes every other day from now on to prevent another bloom. The scientific method is about learning what is happening and why it happens so we can take steps toward a better aquarium, not just put out fires as they arise.

  • Scott Blake



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