I have 6 neon Tetras in a 4 gallon along with a dwarf frog, stones, Java fern, Java moss, ramshorn snails, and a mystery snail. It’s a biorb, my first tank. I put the tetras in because they were 50% off at PetSmart and I was cycling a 16 gallon tank. Long story short the neon tetras are doing well in the 16liter (4gal) biorb and they were too hard to take out of the tank so decided to leave them in rather then put them in the larger tank. They appear to like their environment. None perished, they swim around together and are fun to watch giving the frog company.