Fish for 20 Gallon High Aquarium

Too many fish, too many different water preferences, IMO. I would cut the molly (these are social fish that do better in a group, also prefer harder water than Amazonian tetras and cories), the sword tails (they'll soon breed enough to fill the tank), the red tail shark (6 inch fish with a nasty attitude, not a good choice for a small tank).

The tetras, cories and hatchet fish should work fine together, and occupy all levels of the tank. Have the tank well cycled before adding the cardinals--they are hardy once established, but sensitive to the nitrogen cycle and changes in water. Make sure the tank is securely covered, or the hatchets will carpet surf.

I agree

OrionGirl has a great suggestion on the mix, then you could probably increase the cardinals, depending on how the tank filtration is and how clean you keep it.

8-10 cardinals
6 cories
4 hatchet fish

The swordtail prefers groups, so just one isn't a good idea. OG + Anona came up with a good stocking plan for you IMO -- nice activity at top, middle, and bottom of the tank as OG said.

Is there a particular reason you wanted a sponge filter in addition to the Penguin filter? I think a Penguin Bio-Wheel 125 should take care of a 20H's filtration needs pretty well.

the red tailed shark gets too big i think

If you wanted to add Angels in the mix of cardinals and cories, they'd be fine but only in a bigger tank. When starting with Angels, the least amount of tank needed per Angel is at the very least 1 in a 20 and that IMO is stretching it....my personal preference would be 1 for a 30, then you may have 1 more per 10 gallons up from that.

Angels are too big for that tank. Besides, most angels would LOVE to eat cardinals. Cardinals/neons make up much of their diet in the wild.

my mistake, Leo is right.... I was under the assumption that the Angels would go for neon tetras, not cardinals because the cardinals were a little bigger.... but apparently, they will attack, if not, eat both types. Thanks for the enlightenment Leo


and check me out, keeping Angels for the better part of 10+ years, and I'm still learning