Just got my first 6 fish today. Cycled my 20g tank successfully, went to LFS and we told them we wanted colorful fish like guppies. The dumb rep said that most of the fish can go together, and they would get some new colored guppies in a week or 2, so in the meantime sold us 3 zebra danio and 3 serpae tetras. Getting home I did some research and discovered that guppies are a huge no-no with serpae tetra. I was extremely upset, and planned on calling the LFS to bring back the tetras. I did some more research and discovered how hyper fertile the guppies are, and given this is only a 20g tank, and I am just starting, I really do not want to deal with the myriad issues and over population, so we decided to go with no guppies. My questions are: 1. What colorful fish (if any) would go well with my danios and tetras? 2. Is 3 of each enough? The Danios are having a blast near the top of the tank, but I am noticing that 1 of the tetras is chasing around at least one of the others all over. Should I get more tetras? more danios too? 3. do i need/should I get a bottom feeder like a cory? (will they go well with the tetras?) is it necessary? I like the idea of a fish picking up the extra food that falls, although i'll have to vac anyway to get the waste cleaned. Thanks all in advance!! Just wanted to add, I have polished gravel substrate from petco (fish are NOT from petco), and have malaysian driftwood and silk plants, no live plants.