Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
cardinal tetras- fine, get plenty
CPD'S- even better, if you a looking for more fish rather than larger fish (a good goal with a 20 long. But both species? Maybe not.
ottos- Good! 2-3 are OK, you may need to feed them if there is not enough algae, more would be OK, but they would quickly run out of food.
dwarf groumis- GOURAMI. Only one. They are aggressive and territorial. I would suggest the Honey (Trichogaster chuna) instead of Trichogaster lalius (Colisa lalia). The Dwarf Gourami seems to have too many disease issues to be a reliable purchase any more.
guppies- I would not try for 3 different species of schooling fish, and Guppies tend to be the highest up in the tank, perhaps causing some issues with the Gourami. Maybe not. Some Gouramis are more tolerant than others.
Choose ONE species of schooling fish, and get plenty of them. (Cardinal Tetras or CPDs)
One display fish (Honey Gourami would be my choice, or a Betta)
A couple of algae eaters like Otos
This tank is too small to make a Noah's Ark with a couple of these and a couple of those. Make it simple, elegant.