Water chemistry is one of the hardest things for new aquarists to learn.  I’m going to go through this very slowly and thoroughly.  If you already have a good conceptual understanding of the nitrogen cycle, go ahead and skip this article.   If not, listen up.

There are tons of chemicals you need to keep track of while maintaining a salt water system.   More complex aquariums keep track of everything, and take readings multiple times a day.  New aquarists and ignore the water chemistry to a degree.  You can purchase basic chemistry tests online or in pet stores.  These are the chemicals that your NEED to keep track of:

-          pH

-          Ammonia/Ammonium

-          Nitrite

-          Nitrate

pH represents the power of hydrogen.  It is a measurement of how acidic or alkaline a solution is.  The scale ranges from 0-14, 0-6.9 being acidic, 7 being neutral, and 7.1-14 being alkaline.

Saltwater tanks should maintain a pH of around 8.2 (+/- .2).  In these parameters, ammonium won’t occur.  Ammonium is what ammonia becomes if the solutions pH drops below 7 to acidity.  If your salt water tank drops below a pH of 7, you have bigger problems than ammonium, so I’m not even going to talk about it anymore.   Moving on…

Ammonia (NH₄⁺) is a weak base and is extremely toxic to aquatic animals.   Nitrite (NO₂^-) is also very toxic to fish.  Nitrate (NO₃^- ) is the safest form of nitrogen in the cycle.  It is only harmful to fish at extremely high levels, which is uncommon.  H₂O is obviously water.  All of these will occur in your aquarium at some point.  The goal is to create a equilibrium where ammonia and nitrate are non-existent, and nitrates levels are minimal.  To do this you need to understand the chemical process.

Basically, you need to have a culture of microbials in your system, which convert the toxic states to the non-toxic nitrate state.  The most common mircobials are bacterium, Nitrasomonas species and Nitrobacter species.  These two bacteria work in symbiosis to break the nitrogen down into a safe, usable form for the other animals in the aquarium.  The actual cycle looks like this:

1. Fish waste (urea) + decaying organic matter —> NH₄⁺
2. NH₄⁺  + 2H₂O  —> NO₂^-  + 8 H⁺
3. NO₂^- + H₂O —>  NO₃^-  +  2 H⁺

Nitrasomonas species are responsible for the conversion in step 2 and nitrobacter species are responsible for step 3.  This process as a whole is known as denitrification, and it is constantly occurring in established aquariums.

To reach a equilibrium, you need to have a population of each bacteria that can handle your systems bioload.  Every time you add anything new to you system, whether it is food, fish, or even medication, you increase the bioload.  If you don’t have a sufficient population of these denitrificating bacterium, your system will have a nitrite or ammonia spike, and your animals will start dying.  Dying fish will make it spike harder and you will have an exponential loss in fish.  If you add animals to your system before it has finished its cycle, it is possible that your tank will appear fine in the morning, and everything be dead when you get home from work.  A spike can happen very quickly.  In an established tank, the ammonia and nitrite levels will always be 0ppm.  Nitrates can safely fluctuate between 0-40ppm, but less is always better.

Nitrates will be used up naturally as well.  They are basically a fertilizer for algae and plants.  If you do see spikes in ammonia, nitrite, or nitrate (over 50ppm), you need to do partial water changes to remove the pollution.

In new aquariums, you need to let the tank cycle until you are consistently seeing ammonia and nitrite levels of 0ppt.  Once you achieve this, you can start adding animals SLOWLY.  Start off with a cheap $5 fish, and monitor how it changes the nitrogen levels.  If you keep track of your nitrogen levels on a daily basis, whenever a spike does occur you will know exactly what you need to do to normalize the levels.  In the past article I suggested that you add live rock to your system to jump start the cycle.  I said that because live rock should contain a population of the essential bacteria.  The rock itself will filter the water in an established reef tank.

There are more variables to consider in more complex aquariums, but having a good understanding of this cycle is really all you need to know as an amateur aquarist.

Thanks all for now. I hope you learned something.  The next article on water chemistry will teach you about the other “variables” to consider.