What kind of filter and size do you have and do you have any plants, and what kinds?
The Pygmy Cories are good and 5 is a great number. For the past year, I have been doing my researching and waiting for the new tank which I recently put up so I would have the room needed for a nice group of dwarf Cories! Very excited for this, too!
Two platties can produce a lot of waste, did you say if you know if they are male or female? What color are they? This info is just to get an idea of what colors you have in case ther are other fish which would complement them visually as well as companions. Your tank size limits you in some ways, but makes you be more creative if you are interested.
I always like inverts! You can probably do 3 Japonica Amano Shrimp and a couple of snails if you are so inclined, helps keep things cleaned up.
Red Ramshorns (there many colors) are nice and also Nerites. You can start doing some reading on them if you like any of them. Apple snails no, get too big and Mystery snail maybe one for instance if you really liked the blue or a certain one.
The only drawback on the snails is if you over feed, you'll likely have an over population. Nerites, if you have a female they will lay individual white eggs around the tank, but they need brackish water to actually reproduce. I have a female and it does lay eggs around. For me not a big enough reason to get rid of her! She eats lots of algae and keeps the tank clean.
My Amano Shrimp are hilarious and I think totally worth having as much as fish or more so!!! Although people call them Algae eating shrimp, they are scavengers and love meaty foods too!
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