Hiya abelo and welcome :)
Couple of things. Your tank is pretty small, and as such is difficult to maintain water parameters. A small ammonia or nitrite spike in a big tank isn't that big a deal; in a small tank can be deadly. COnsequently, small tanks need a LOT more work keeping on top of water parameters. Frequent testing is a must, even after the tank cycles.
You really don't have much room in there for a lot of fish; those 3 you chose puts you close to your max bio-load. The bloodfin tetras will get to be about 2 inchs long, mollies about 2.5 inches and the swords around 5.5 inches. Plus, I believe they are schooling types fish. You may want to stick with the tetra, and have a small school of 3 or so in that tank (and maybe an oto for algae or a cory or 2 for bottom cleanup). The mollies and swordtails would quite possibly breed themselves right out of the tank LOL
Your tank is just starting to cycle. You may want to double check those ammonia levels, by either using a diff test or asking the lfs
to check it for you. Impossible for nitrites to show up without ammonia showing up first, although there is a small possibility it has spiked already (somewhat doubtful in a tank that new tho). Nice write-up on the nitrogen cycle here: http://faq.thekrib.com/begin-cycling.html
. Keep in mind, ammonia and nitrites are deadly to fish; ammonia burns the gills and nitrite competes with O2
. Both suffocate the fish. Wait until ammonia and nitrites are zero before adding more fish, or they will be starting at a great disadvantage.
Obviously, that may NOT be the cause of your poor dead fishies. One or both may have also been sick coming from the store. Unfortunately, there is no guarantee the lfs
has your best interests in mind, or even the fish's. Its a business, and thats the top priority (for the most part; there are some amazing lfs
out there, but they are few and far between). I strongly suggest you do your own research and continue to throw questions at us. Just as you wouldn't buy a car without doing some research and price comparisons, don't depend on one lfs
for your info. The cycling website I posted has lots of other pages that might be of interest to you; you'll see the links to other bits of info at the bottom.