hiya,
welcome to TFF and to fishkeeping
for starters I'm kind of glad your not wanting to kep the goldfish, they can actually get very big and would need a much bigger tank, howevere your 29g would make a lovely tropical community tank so I think your definately heading in the right direction.
please forgive me if i'm telling you things you already know, but as i think your an absolute beginner i'll go through some of the basics with you.
the absolute first thing you should buy when your keeping fish is a water test kit, have you got one? If not I recommend the API FreshWtaer Master Test Kit, they're readily available, fairly cheap, easy to use and quite accurate (lots of test kits are awful!)
so if you've got a test kit tell us what your test results for ph, ammonia, nitrite and nitrate are.
do you know anything about the nitrogen cycle and cycling a tank?
the absolute basics are your fish create ammonia in they're waste, this is toxic so it must be removed from the water, this is what your filter is for, there is nitrifying bacteria living in there who convert the ammonia into nitrite (also toxic) then to nitrate which is much safer, you keep this at a manageable level through doing water changes every week.
the main problem with new fishtanks is that the filter's don't come with the bacteria you need. they can't live out of water in the sponge on the shelf in the fish store, however they are all around us, and will relish the opportunity to grow and develop when they find a nice safe home (your filter) and a source of food (fishy waste). the problem starts becuase when you add fish to your tank you will have a very very small amount of bacteria, they take a while to grow and multiply to the point where they can eat all the waste from your fish. so for the first few weeks of putting fish in the tank the bacteria are growing and will struggle to keep up, so you get toxic levels of ammoni and nitrite in your tank, this can lead to death or disease.
in the past this was alwasy countered by putting in some very hardy fish at first and hoping that they would survive the toxic levels, then when the bacteria had built up after a few weeks you could add more sensitive fish. however this really wasn't very fair on the poor fish who had to start the tank off, I dread to think how many will have died.
so in the last 3/4 years a new technque called fishless cycling has developed, this is where you add pure ammonia to the tank to grow the bacteria on until they are at a point they can handle the fishes waste, and then you add your fish when it's safe for them. this is detailed in a pinned topic
here, have a read.
so that should tell you why the first thing you need is a test kit. if you don't know what level of ammonia, nitrite, or nitrate you have in your tank, you don't know if you have enough bacteria to keep the tank going or if you need to do anything else.
Now I know that's a fair bit to take in but it should be your starting point. so digest all that and let us know what your water test readings are, then we'll tell you what the next step is and what fish could be suitable for your tank.
