Yeah, whenever any unwary visitors comment on our tank, we unleash the fish nerdery on them until their eyes glaze over.
Ok so more fish nerding after running the post by Langston/Ugzug, who is the true fish guru in our house. The tank is really more of his hobby, and I learned all that stuff by proxy. He says your filter is pretty common. It will take "EZ change replacement filter cartridge size 3", and can be found at
Walmart for $4.50, apparently. He says you can probably just rinse out the components when you do a water change. If you can get most of the crap out by rinsing, then maybe replace it every other or every 3rd water change. Since your filter doesn't have any sort of biomedia, you'll really need to do a partial water change semi monthly to keep all your chemicals in line. He says 25% is adequate. You'll probably want to put an aeration system in the water. Some sort of bubble stone. You buy cheap air pumps and either a stone, or one of those bubble ornaments (deep sea divers, or treasure chest thing). Stick with the silk plants for now. Live plants will die on you without the right lighting system. Langston also says silk plants are "an algae nightmare", so you might want to consider replacing them with plastic, which is more easily cleaned, or plan on replacing them every 4-6 months. If you add decorative rocks, stay away from limestone or granite as they leech chemicals into the water. Stick with river stone or drift wood for decorative aspects, and make sure you boil them thoroughly before adding them to the tank. Additionally, if you DO add a piece of drift wood, it will leech tannins into the water and turn your water brown for a while. You can help lessen this effect by soaking it in a pot of fresh water for a few days. The water color will come back after some water changes. Driftwood is nice if you put any sort of pleco in the tank. They love the drift wood.
He also says to avoid any sort of African cichlid fish. The water chemistry they require will be totally different, and they'll just die on you. Additionally they tend to be more aggressive. Angelfish fall into this category. For the recommended fish list, Langston also adds
rummy nose tetras, any kind of
rasboras,
serpaes,
glow-light tetras. Fish to stay away from: Anything over $20. If it's expensive, it will require increased care, and your tank is probably not large enough for that variety of fish. Keep to the cheap fish. Also avoid
"Chinese algae eaters" aka "flying foxes". They tend to be aggressive. They are sometimes mislabeled as "Siamese algae eaters" in pet stores because the two breeds look almost identical, but unless you're positive the employees know the difference, avoid them. Stay away from
tiger barbs,and
knife fish(which is a bummer, because they're pretty cool looking).
You will need to have some form of algae eater or bottom-feeder. For algae eaters, avoid any catfish. They get too big, and they'll eat your small fish. A catfish can and will eat something half it's size. Stick with plecos or
cory cats (which are not catfish). Also, despite common perception, snails are ok too. You can get a "mystery snail", which are a pale yellow, and they'll be ok. Just get one at a time, otherwise you'll end up with several thousand "mystery snails". :P Snails will last about a year, maybe a touch longer depending on your temperature. They're cheap and a neat addition to the tank. Shrimp, like the
ghost shrimp are cheap and neat to have... but their life expectancy is very short. They're more of a novelty as opposed to any sort of true addition to the tank. An interesting algae eater, which may be hard to find, but definitely unique is the
farlowella or "twig catfish", which are safe despite being called a catfish.
A note on "aggressive fish". Most of them are territorial. They'll carve out a section of the tank for themselves and that will be THEIRS. It's typically around some form of ornamentation or large plant. If you DO decide to get one of the semi-aggressive fish, just make sure they have a specific area to hide in and call their own (your castle will probably be fine). You also need to add them AFTER the community fish are established. Make them the new-comers to the tank. Buy them as small as you can. If you do decide to buy a gourami (they are very pretty fish, afterall) try to find a dwarf or kissing gourami.
Some fish stores will have little fiddler crabs or blue lobsters for sale. Crabs are air breathers and will need some way to get up and out of the water to breath, so in a full fish tank, they aren't ideal. Blue lobsters will eat your small fish and are pretty adept at catching them. You do not want to put a blue lobster or crayfish in the tank with any kind of bottom-dweller (algae eaters, plecos, and cory cats). Guppies are safe as long as the blue lobster doesn't have any way to crawl up to get them. Guppies tend to live in the upper 1/3 of the tank. In general though, it's probably better to stay away from the crustaceans unless that's ALL you have in the tank and your tank is specifically geared towards them.
If you're looking for fun fish, something interesting or eye catching, Langston recommends the loaches that I talked about earlier, or some of the fancier breeds of mollies, like lyre-tail mollies.
As far as water chemistry goes, for this set up you'll only need to really worry about pH. You'll want to pick a pH test kit and try to keep it between 6.5 and 7.6. Optimally, it should be at 7.0. You'll want to avoid wide, quick swings in pH. If your pH needs adjusting, you'll want to do it
gradually. Number one thing that kills fish is pH swings. Test the water when you do water changes. (On a side note, this is all Langston adding this. When I kept little cheapy fish tanks, I never bothered with any sort of water tests... but if you start losing a ton of fish for no real apparent reason, then consider looking at your pH. Could be out of whack and contributing to the loss.)
A quick note on food, then I think I'm done with the fish nerding. For your fish tank if you're just doing mollies or tetras, you're fine to use the standard Tetramin fish flakes, found at Walmart or any pet store. If you add a pleco as your algae eater, you need to put a piece of driftwood in (can be a small piece) and probably add an algae wafer every other day. Other algae eaters (cory cats and the like) will supplement off of the flakes. Don't feed your fish more than you'll eat in about 2 minutes. Overfeeding will make your water disgusting quickly. If you DO end up doing a crustacean or amphibian of any kind, you'll need to do shrimp pellets. You won't need to bother with any sort of live or frozen food for this set up. It tends to be heavy in fat. Your fish will LOVE live/frozen food, and it may help enhance their colors (especially blood worms), but it needs to be a treat, not their staple. You also run the risk of the rare parasite that fish can pick up from bloodworms, so use them sparingly, if at all.
Total overkill for what you are looking for, I'm sure, but once the topic is opened, we kept thinking of other things to add to it.