Hello i am James (as u will of already guessed) and i am just wondering what would be the best fish for a 20 ltr fish tank when its already occupied by 3 guppies?
What gender guppies do you have? I wouldn't add anything, really...a 20 liter tank is not big enough for much, and if you have females and males, you will end up with a slew of fry.
Agreed with the above, it's quite small for more fish. Also, it would likely not be the best situation for female bettas either, they can be fairly aggressive with each other and two isn't usually sufficient to reduce that aggression.
What gender guppies do you have? I wouldn't add anything, really...a 20 liter tank is not big enough for much, and if you have females and males, you will end up with a slew of fry.
There are invertebrates that would work--any of the grazing shrimp (amanos, cherries, etc, just avoid the filter feeders) or snails that would work well, but I wouldn't add any fish.