Tuesday, June 11, 2013

Keeping Fish and the Aquatic Nitrogen Cycle!

Location: Salt Lake City, UT, USA
I don't know about the rest of you, but I love fish!  I have been an avid enthusiast and hobbyist since I was young.  My father and I were both introduced to the hobby at the same time, on a whim stopping in a pet store where the manager was a Cichlid fanatic.

Marlin the clownfish
One of the big barriers to keeping fish is knowing how to keep them alive.  Unfortunately there is a lot of misinformation about keeping fish out there.  Really, to keep fish, you only need two things besides the obvious of water and something to hold the water.  You need to regulate the temperature (usually a heater is quite sufficient), and you need to filter the water.  I've already said about all there is to say about regulating temperature.  The only thing to add is that some tanks, usually with very powerful lights, will require chilling instead of heating.

Marine aquarium filtration (salt water)
There are several types of filtration: mechanical, chemical, and biological.  Mechanical filtration is what most people think of when they think of filters.  This involves physically trapping non-dissolved matter, usually in some sort of mesh.  Though this does a great job of removing larger visible impurities, the primary benefit to mechanical filtration is that it can help keep your water more clear, which makes little difference to the fish but can increase your enjoyment in watching them significantly.  Mechanical filters can range anywhere from a foam pad, to a micron filter further reduced by diatomaceous earth, the latter of which will even filter out mid-water algal and bacteria blooms, and even a method called foam fractionation which is used in marine aquariums.

Chemical filtration uses substances that absorb impurities from the water.  The most common substance used is activated carbon, though other substances might be used depending on what chemical absorption is required.  This can appear like biological filtration in some regards, you can remove some of the same substances that biological filters take care of, but it accomplishes this by absorbing the impurities.  What most people don't understand about chemical filtration is that it is a band-aid for a real issue.  There is no way to know how effective it is being, and once it fills up, it starts to leech chemicals back into the water.  Chemical filtration, in my opinion, should only be used for very short periods of time between changing (8-24 hours) in emergency situations while you are working to fix the underlying cause of the issue.

Cleaner shrimp working on a polyp coral
So that leaves us with biological filtration, the core of keeping fish, and the core of biological filtration is something called a nitrogen cycle.  Understanding this is really the key foundation of keeping anything alive that lives in water.  It's all you really need to know to keep freshwater fish alive, and the first stepping stone toward keeping marine fish (salt water) and invertebrates, like corals and anemones.  There are a lot of things that go into water, but true waste is primarily nitrogen, in the form of ammonia.  Even uneaten food and dead organisms rotting are ultimately producing ammonia.

Ammonia is a poison to fish, and a high enough concentration will lead to all sorts of problems resulting in a dead tank.  We MUST filter this out!  We look to nature and find that there are aquatic bacteria which actually eat ammonia!  Nitrosomonas basically eat ammonia and produce another form of nitrogen called nitrite(s).  This form of nitrogen is not as toxic as ammonia, but is still a toxin in a fish environment, and must be removed.  Again we look to nature and find another little aquatic bacteria called Nitrobacter which eats nitrites.  Like it's cousins, Nitrobacter produces a nitrate as a byproduct.  Nitrate is a substance you might have heard of before.  It is a form of nitrogen commonly used in fertilizers, and is relatively non-toxic.  This whole process of converting ammonia to nitrate is the nitrogen cycle, and basically all life depends on it.

Understanding this transfer from ammonia to nitrite, then nitrite to nitrate, is the foundation for understanding how nature filters water.  But how do we apply this to our tanks?  We look at how these bacteria live in water, and we find that they flourish best when they have a lot of surface area to colonize (rocks and sand perform this in nature) and a lot of oxygen, which in aquatics means swift moving water with a lot of surface agitation and a large area for exchange with the air.  So in your aquarium you need good water to air surface area (go wide or long, not tall), have good water movement (most fish really want a lot more than most are given), and agitate the surface a little.  It is not the air bubbles rising that help get air in water, it is their breaking at the surface that helps promote gas exchange.

20 gallon long, a lot of surface area.  Notice the rippling effect, great for gas exchange!
Provide a lot of surface for bacteria to live on.  Under-gravel filters of days-gone-by use the gravel as an actual medium for bacteria to grow, but those filters tend to trap waste under the filter plates and it never gets removed, and the flow is not strong enough to provide oxygen.  This results in an anaerobic (non-oxygen breathing) bacteria colony, which you do not want.  Instead, fill the tank with porous rock, with a lot of surface area, and get good Powerhead style pumps to keep things moving.  Lace and some lava rocks work well, I suggest you consult with your local fish store to pick out the right rocks that won't leech bad stuff in your water.  There are also a lot of filters that provide mediums for bacteria growth, from Marinelands power wheels, to bio-balls, and canister inserts, but I prefer to stick with the more time tested approach of having the system support itself (I do advocate sumps, separate tanks hooked together, to help increase water volume, and move some of the bacteria supporting rocks out of the main display tank).

Armed with well oxygenated water, good strong water flow, and plenty of rocks for bacteria to colonize, your tank will process its own waste into harmless nitrate that can be removed by aquatic plants, or with regular water changes.  Failure to remove nitrate can lead to algae growth.

Aquarium Sump
A few things to keep in mind.  Bacteria takes some time to grow, and will not grow until there is an excess of food (ammonia and nitrite).  When first starting out it is important to understand that you will have to cultivate this bacteria up slowly as the tank matures.  This initial 'cycle' typically takes 2-3 months (but can vary from 1 month to a year, it all really depends a on a lot of factors, assume 2-3 months).  To get ammonia in the tank you need something alive.  Just one fish per 20-40 or so gallons will work well, assuming they are fairly small, less if they are larger fish, and you should already have a vision for what you want in the tank, so you should know which fish to get (least aggressive variety is best to start with).  Get a test kit for ammonia and check it every 3-7 days.  You should see the ammonia go up, and plateau for a week or two.

You should be like a month in already and be frustrated at how boring your tank is so far.  That is OK!  Just sit on that emotion and in the end you will come out with a work of art and a piece of pure beauty that everyone ooh's and ahh's over.  Get a nitrite test kit and you should start to see that the nitrite is going up slowly.  Keep an eye on the nitrite, and watch how after a week or two the ammonia has dropped down to fairly safe levels as the nitrite rises.  You could add a few more fish at this point, but only a few, go really slow.  The nitrite will go through the same pattern which ammonia did, it will plateau, then start to drop as new the bacteria colony grows to consume the excess resources.  You want to get a nitrate test as well, and again, you can watch nitrate rise as nitrite fall to safe levels.  Once this is done you have 'cycled' the tank, and have a full nitrogen cycle going on!  Pretty cool huh?

A little Blenny!
Again, go slow from here.  each time you add more fish that ammonia is going to spike again, more bacteria will grow, ammonia will drop as nitrite grows, then nitrite drops as nitrate grows.  Too much of a swing and your fish will suffer, and likely get sick.  So take it slow, give yourself a good year, maybe even two, to fully stock the tank, and you will end up with something you love instead of an algae infested death trap that you loath to look at.

Six-Line Wrasse

If you have any questions about fish or fishkeeping, ASK!

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