Rule Number One: Fish don’t like distilled water.
I bought some distilled water yesterday, thinking it was the right thing to use when replacing and refilling the water in Blinky’s tank.
I was very wrong.
I watched him struggle yesterday and not eat food. I worried when (even before the water change) that he was listless. After the water change, I ignored him as I piled through work.
It’s the first pet I’ve ever had on my own. I had a dog when I was very young (like 3 or 4) and it was taken away after it bit me. At least I think that’s what happened. Now after only a few weeks, this fish is dead. Do I get a new one? Should I get a bigger tank?
Thoughts?
Steve Kirks 
Depending on the type of fish you’re trying to keep, it can actually be more difficult to keep a very small tank rather than a larger one. Many people recommend starting out with a 15 or 20 gallon tank. A tank that size has a little bit more “inertia” with regard to chemicals/salts/air/etc. in the water.
I can’t find an older post that says what type of fish Blinky was. If he was a gold fish, his tank should have been 10g or so (goldfish need a lot of water, even though many people keep them in very small tanks). I’d also be curious to hear what your care structure was like. With a larger established tank, you can get away with longer time in between cleaning, however with smaller tanks you have to be careful.
Assuming that you’re interested in freshwater tropical fish, the following might be helpful. There’s a cycle that happens with a new tank. At first, the tank has no bacteria in it. You’re supposed to only have a few fish in order to start the cycle, maybe 1/4th what the tank can handle. Set everything up, making sure that if you use tap water you give the tank a few days with some water conditioner and no fish for chlorine, etc. to work out of the water. For the next couple weeks, you’ll want to do frequent partial water changes. Fish waste is NH3 and is poisonous to the fish. Initially, the lack of bacteria will cause this waste to build up, so you’ll want to do frequent partial water changes at first (partial so you don’t remove your developing bacteria from the tank!). As the bacteria develops (in the stones and filter of the tank) it will begin converting the NH3 in the water to NO2- and NO3-. Once your tank has cycled, you’ll want to maintain a cycle of partial water changes, however it can be much less frequent.
It’s important to note that when you mess with the tank (clean waste from the stones, or change the filter) you’ll disturb the bacteria colony and may cause a partial cycle.
A good summary of the tank cycle can be found here: http://faq.thekrib.com/begin-cycling.html
The bottom line is that keeping fish is very rewarding: they’re fun and interesting. However, it can be a little tricky at first. Keep at it! As you learn more, it becomes easier!