First off, welcome to fishkeeping. We just restarted our 29 gallon aquarium and I do have 6 danios in there. They are great fish but I agree with BlaseMrNiceguy they are super active - like 2 year olds in a candy store on a sugar rush. You do need to cycle first. There are a few ways to do this - you can use an ammonia source or you can crumble up fish food and add a bit each day to let it begin decaying and releasing ammonia. Both ways have their pros and cons. I've only cycled using the fish food method and I also added some nitrifying bacteria that I bought at only local fish store that actually have people who work there who also keep fish and are knowledgeable. The rasboras are a good suggestion and they are very beautiful fish. In addition to the 29 gallon I have four 10 gallon tanks. In three I have a single male betta fish. My husband's initial objection to this was that one fish for ten gallons? Talk about a dull tank but I guess one male betta is like one potato chips and he's the reason we actually have the other two. Each of my 10 gallons have fake plants (we are switching to live plants soon and my 29 gallon is planted) and a sponge filter. The sponge filters are super cheap and easy to maintain. You can also but a regulator valve on them to control the strength of their output as Bettas like still waters. They are full on personality. I've also read others stating that they've started a female betta sorority in a 10 gallon with much success. Our fourth 10 gallon has about five platties in it. Anything too active and the 10 gallon just isn't enough space to swim around. Personally if one of my platties died I'd be a little upset, to lose a danio would worry me as to what's going on in the tank but lose one of my Bettas and I'm heartbroken. Each of my boys have their own heaters, Betta hammocks, Indian Almond leaves, and floating ceramic logs to hide in. I guess I just found my perfect fish! What I would suggest to find out which fish would best suit your personality and what you would most like to get our of your tank is to do a web search for Intelligent Aquarium Advisor. Get our your measuring tape and put in the dimensions of your tank, what brand and size filter you have, etc... and to check the box that says "show species only suitable for my tank". This should give you lots of options and will tell you how many of a certain species of fish you can stock in your aquarium and what your weekly water change will need to be. Before you begin the research though I would go ahead and invest in a good liquid chemical water test kit (approx. $30 - $35) otherwise you won't know if the tank has cycled and how far along it is and do some searches on fishless cycling - don't do the paper strip tests as they are notoriously inaccurate. Don't get impatient while waiting for the tank to cycle this is the time to window shop and discover your options. I would check out my local fish stores. Find one with employees who actually keep fish. If they start quoting you the one inch per gallon of water rule I would ask if they actually keep fish. The species activity level, behavior, species natural habitat, and your tank dimensions, filter size, etc... all come into play not just how big a fish is. If you can't find anyone at a local fish store who knows anything about fish then don't worry just make a short list of potential candidates and research. I would still go back into the fish store though to evaluate who has the healthiest fish and who has what species of fish available. Always ask too- just because they don't have a species in stock doesn't mean they can't order it for you. You are starting off right by doing your research first. Just don't lose patience check out that fish calculator to get your short list going. I would also follow BlaseMrNiceGuy's advice in at least looking into doing a planted tank. The only problem I have with this is that personally I bought the 10 gallon aquarium kit a few years ago that came with a filter, hood, etc... To get the tank the way I want it for a betta tank I pulled the filter out and bought a cheap $10 sponge filter, bought a heater, and now I still need to replace the hood to get the flourescent lighting for an artificial sunlight bulb. If you've already bought your 10 gallon in a kit you may want to limit yourself to fish that can take a stronger current and go with artificial plants. Live plants too usually require some type of fertilizer (not expensive) so it really depends on your budget and what you want to get out of your tank. The good news is though that in the long run going with live plants will save money (the bulbs last a LOT longer than the little incadescent ones and you don't have to constantly replace bad looking plastic plants or suck out your gravel with a planted tank plus I think it looks a lot better). If you've already bought your 10 gallon in a kit and don't want to spend additional money to go with a different hood/bulb and /or filter then I would buy whatever plastic/silk plants you like best and get the rasboras or platties. The platties I keep and can tell you they are hearty, come in a wide variety of colors, and are livebearers. Don't worry though the adults will eat the fry so you won't get overrun but if you want to get a larger tank later you can move the adults into the big tank and keep the 10 gallon for the fry allowing them to grow and mature (just make sure you fryproof your filter so they don't get sucked in). They are friendly little fish, eat like pigs, and are fun to keep. They are hardy, great for beginners, don't require a lot of upkeep, and can tolerate high PH levels. The ratio should be at least 2 females per male. They love a heavily planted (either artificial or real) and should have plenty of hiding spaces. A good cheap "cave" or hiding spot is a brand new, never used terra cotta pot turned sideways or a new glass or coffee mug turned sideways. I hope this helps, welcome to fish keeping, and I apologize for the book.
