At some point in the past, I took the time to write down for a friend all kinds of things I had learned through the years with my aquarium. When I have the time, I intend to dig that old email back up and post the information here, but until then, I'll post these more recent email notes I wrote:

The one thing you most need to be aware of when setting up a brand-new aquarium is the nitrogen cycle that new aquariums go through. I didn't know they had this cycle when I first started out; I figured you had a box of water, stuck fish and tangible supplies (like a heater and filter) in it, and they'd be fine. Nope!

I went through several years of problems with my tank, and for some reason no one ever told me about aquarium chemistry, until I finally complained to the right person. If I had met him in the beginning, it would have saved the lives of countless fish and hairs on my head.

What you need to know, basically, is that the aquarium is not a static object; even though it may be small and in your house, it's a living ecosystem, and that means things are changing inside it that you can't see, affected by each other. The cycle goes something like this:

1) You start with clean water, into which you add fish.

2) You feed the fish. Some uneaten food falls to the bottom of the tank. The fish poop. That joins the food at the bottom.

3) The uneaten food and poop begins to break down into ammonia, which is toxic to the fish.
In an established tank, this isn't a problem due to the presence of tiny organisms that break down the ammonia into less-toxic substances. But this starter tank has fresh clean water, with none of those helpful bacteria. So the ammonia builds, out of control, and some fish may die.

4) Eventually, the bacteria do find their way into the tank (if there is food for them, they will come!), through the air and possibly the water that you bring fish in from the store, and they set up a colony and begin breaking down the ammonia. But it takes a while for that colony to reach a size sufficient enough to handle the amount of ammonia that is being produced. This step in the cycle can be aided by getting some water from a friend or someone with an established aquarium in the beginning of setting up your tank - you'll have a head-start on setting up your bacteria colony. Even better might be to get a piece of sponge or bio-ball that's been in their filter for a while, slimy with bacteria. It's also a good idea to only start with around three fish so that there isn't a large volume of ammonia being produced initially.

5) The next stage is the Nitrogen stage. The type of bacteria that breaks down ammonia converts it to nitrites, which isn't too healthy for your fish, either. It takes a while for the nitrogen-producing bacteria to do their thing, so at first, there's nothing to attract the second type of bacteria, usually until the tank has a spike in nitrites; I think that at first, the nitrites are produced faster than the bacteria can reproduce. This is the key; in each stage, you are trying to reach an equilibrium: the right amount of bacteria present to handle the amount of toxin being produced.

6) The last stage is when enough of the second type of bacteria have been attracted to handle all the nitrites produced by the first type of bacteria, and the nitrites are converted into harmless nitrates. When the nitrite levels fall and the nitrate level rises, the cycle is complete. The tank is ready for more fish.

But! Don't run right out and buy a ton of new fish; your bacteria colonies are now present and working, but they have stabilized at a size to match your current population of fish and their by-products. When you add more fish, the amount of by-product will rise, so it will take a little time for the colonies to grow to the new correct size.

For more information with visual aids and everything, check out these sites:

Both of those sites are very good at explaning the cycle even further than I have, with the second one getting into more technical detail.

1) As a general rule of fish, if one can fit in the mouth of another, it will end up there.
For instance, Angelfish eat mollies and neons and other small fish. If you have an angelfish, it will determine the smallest size of fish you can have. Some are tricky - I was really taken in once by this very cool Butterfly Fish I saw at the store, examined his mouth size, determined he was okay, and took him home. The guy at the store also assured me he would behave himself. I had to ask because he was definitely larger than some of the fish I already had. Well, neon tetras very rapidly started disappearing, I finally caught him opening his mouth one day - to my surprise, it was much bigger than it appeared when closed! Needless to say, he went back to the store.

2) Beware of getting a pair of livebearers (mollies, guppies, platys, swordtails, etc.), or of buying one female from the store who is already pregnant. They WILL breed and make lots of little fish. At first it will be fun and cute. Then some will get eaten, but if enough grow up, you will eventually find yourself trying to give them away to friends and pet stores, which quickly becomes a pain.

You can tell the difference between a male and a female livebearing fish. The female has a typically-shaped anal fin (the one under and forward of the tail). The male has that same fin, but he has a thin extension on the top-back of it that brings to mind the idea of a penis. He does use this extension to funnel sperm over to the female. I used to catch my male mollies sideling up to the females with an obvious, "Hey, baby!" (poke-poke-poke), and the females, in typical female fashion, would glare at them and swim quickly away. Though apparently not quickly enough!

3) If you want a Betta/Siamese Fighting Fish, you can have ONE. More than one will tear each other up. They will be ragged and not pretty. A single one will leave most other aquarium fish alone except for, in my experience, Paradise Fish, Dwarf Gouramis, and Blue Ram Cichlids. I sometimes have one betta with a blue ram in my tank, though, because while they do pester each other and chase each other around the tank, they don't seem to actually hurt each other, and sometimes I think they're just egging each other on, playing tag. They're fun to watch, and having that element of competition around makes the blue rams more colorful.

4) I don't recommend buying painted Indian Glassfish. They are artificially colored with ragged-looking neon stripes (yellow, pink, blue, green, purple). The process makes them weak, so they get sick and usually don't live very long. They often have have very obvious "ick" or "ich", a fish disease that appears as tiny white specks on their bodies. If they do survive, they eventually lose the fake coloring and are just transparent. I like them that way and, after much searching, finally found some un-painted ones for sale. I bought five plain transparent Indian Glassfish to go with my transparent Glass Cats, and over a year later, they're still going strong.

5) Look at fish closely in the tanks before you buy them - make sure they don't have ick. You don't want to bring that home and spread it around to the rest. The scientific name of ick is Ichthyophthirius multifiliis. Buy some ick medicine to have on hand in case of a sudden unexpected outbreak in the aquarium, because it will happen at some point. If you have to use medicine in your tank, you must remove the charcoal from the filter, so it can be kind of a pain that I prefer to avoid, if possible, by not buying ick-y fish.

6) If you have a large tank, I highly recommend getting a Fluval canister filter. The one for my 55 gallon tank costs around $130. We used to have an older one, and it was hard to get all the air out of the lines after opening it up to clean it. This new one is much better about that.

7) Don't set the aquarium up near a window. The sunlight streaming in will create a happy place for algae. Algae will grow eventually, but the more light it has, the faster it will grow. If you want live plants, you can get them, but will most likely end up replacing them every once in a while. I have never successfully kept live plants for a long time. They eventually get ratty-looking, and algae grows right on them. If you have an expensive light set-up with bright lights over the tank, you can grow plants in it, and if you manage to reach a certain equilibrium in the elements in your tank, the plants will use up all the nutrients that the algae would otherwise be living on and you'll have nice plants and not much algae, or so I've heard. I haven't had the energy or the money to spend on trying to set up really good lighting to see if that's true.