What is the nitrogen cycle?

The nitrogen cycle, or cycling process, is the nitrification of your aquarium where beneficial bacteria form to consume the harmful types of nitrogen. When you begin a new tank, you will go through the nitrogen cycle. Fish waste and uneaten food break down into the first phase of nitrogen, ammonia. This is the most toxic to fish and gets dangerous at even low levels. For the good bacteria to begin to grow, there must be some level of ammonia.

Unfortunately, one usually becomes aware of the nitrogen cycle after a tank has been set up and stocked. Fish begin to show signs of disease or die mysteriously, and your tank has only been up for three days! 90% of the time this is due to high levels of ammonia poisoning your fish to death.

There is hope, however. Change out 10 to 20 percent of your water daily. This removes some of the ammonia and the new water helps the fish get through the nitrogen spike. Contrary to what you may read elsewhere on the Internet, water changes are a must during the cycling period (unless you're fishless cycling) and do not prolong the process. The ammonia is being colonized in the gravel, on the glass, in your filter bed, and even on your plants. Changing water does not impact the growing good bacteria.

Once a sufficient group of bacteria has formed, the ammonia is transformed into nitrite. This is a byproduct of the ammonia-eating nitrobacters, the good bacteria. Nitrite is also bad for fish but not as deadly as ammonia. Nitrite affects your fish's ability to regulate oxygen, so you may see your fish gasping for air, hanging out near the filter return, or appear red around the gills or just plain listless. Adding a small dose of aquarium salt is a temporary solution for nitrite and can help your fish get through the spike. Once again, water change, water change, water change.

To review, fish waste + uneaten food = ammonia, which then = nitrite. Elevated ammonia always follows elevated nitrite. Though not as lethal, nitrite is bad news.

The finish line in the nitrification process is to reach 0 ppm ammonia and nitrite (ppm stands for parts per million and is measured with water test kits). When both drop to zero, the tank is cycled, and the final form of nitrogen is present.

This is called nitrate.

Nitrates are only removed with water changes. They are not deadly unless in extreme quantities, and a healthy freshwater aquarium always has some level of nitrates.

Do I need test kits?

If you want to keep a successful fish tank, then the short answer is yes. However, if you're trying to cut costs, then you're probably only interested in the bare minimum in getting by. Ammonia and nitrite test kits are absolute musts. pH is also good to have. A nitrate test kit can be a bit harder to find, and is also more expensive.

What water should I use?

Generally, plain old tap water is fine. You must add a water conditioner to remove the chlorine/chloramine. If you live on well water, obtain a pH test kit and see where you're at. Mid 6 to 8 should be fine for most fish as they can adapt. Never use the pH buffer chemicals. They only cause problems and make water changes super complicated.

Unless you're keeping a marine tank or trying to breed discus, I do not recommend reverse osmosis water. All the minerals and trace elements have been removed. Also, the pH is 6.0, and if you ever do a water change with regular tap water, you'll have a huge fluctuation.

How many fish can I keep in my tank?

Often 1" per gallon is quoted, but this is only a rule of thumb. Many variables come into play here, including the size and dimensions of your tank, whether it has live plants, and what kind of fish you're stocking. 1 inch of kuhli loach is going to be much less on the bioload than 1 inch of goldfish. Larger fish make more waste than small fish, and generally, you can overstock when you're keeping small schooling fish like tetras. To give you some idea, I keep over 20 small schooling tetras and kuhli loaches in my densely planted ten gallon tank. I also keep countless guppies in my java moss-planted three gallon. Live plants consume nitrate, and thus you can stock more small fish.

Is my guppy pregnant?

I'll go out on a limb and say yes. If a female guppy was in the same tank as a male, chances are good she's knocked up. Look for the black or brown spot in her abdomen. This is called the gravid spot and is always present. It is larger when the guppy is pregnant, and her whole abdomen expands as she gets closer to giving birth.

Can I keep bettas in a community tank?

This depends. Female bettas generally make good community fish. They are slow swimmers, and if they are aggressive, most fish can outswim them. Some females tolerate other females, some do not. It all depends on the fish.

Under no circumstances should you keep more than one male betta in any given tank.

I've had luck keeping male bettas with schooling tetras. Fish that should not be kept with male bettas are guppies, angelfish, gouramis, or any slow-moving fish with a long tail. Also avoid barbs and other nippy fish.

I saw freshwater crabs at the LFS. Can I put one in my tank?

Fiddler crabs need access to air and are escape artists. They also do best in a brackish water aquarium, that is a tank with a specific gravity (salinity measurement) of 1.008. They can be kept in freshwater, but in many cases they will only live 2-6 months. You must provide them a way to get above the water, and the aquarium must be completely covered. Otherwise, they will escape every time.

There are also red claw crabs. These are sold as freshwater crabs, but this is open to debate as well. Some people say they are brackish, some say they are totally fresh. My advise would be to research each school of thought and make an educated decision on what is best for your crab.