About 60l.
I have a couple of albino corys, 9 neon tetras, red tail shark, 3 half backs, 1 juli cory, 5 platys, 3 glass catfish and 5 lampeyes
you've got way too many fish in there as is, to be honest. Some aren't really suitable for your tank size. I'm guessing you stocked them looking at their size in the store, but then look at it in adult size:
albino cories: 3 inches as adult, need to be kept in groups of 6
neon tetras: about 1.5 inches each, they'll be fine
Red Tail Shark: very territorial as an adult, may bully and harass your other fish to death when he grows up, should be kept in a tank 4 feet long to claim territory and not beat on other residents
Half Beaks: don't know anything about these to be honest, not my cup o tea
Julii Cory: once again needs to be kept in groups of 6, gets 2 inches long
platies: Get about 3-4 inches long, and are very bulky rotund fish, you've got way too many of them in a tank your size
Glass catfish: Somewhat fragile species, should be kept with only docile fish, may be a good candidate to be killed by your shark. Should be kept in groups larger than 8 to feel comfortable, when kept in small groups they may die for unknown reasons or go on a hunger strike. can get 4 inches long.
Lampeye Tetra: get 3 inches long, generally docile, but can be nippy to other tank residents when kept in small groups.
If you ask me, you need to remove a lot of these. Rehome the red tailed shark, glass catfish, lamp eye tetras, get rid of 2 or so of your platies (though they might not even be good for a tank your size, I don't really like livebearers so I wouldn't know) get a few more cory catfish, and then think about a centerpiece fish.
To answer your original question, you could look into dwarf cichlids. If you ask me, a pair of bolivian rams or male and 2 female apistogramma cacatuoides would work just fine in a tank your size. But not both. Your tank size is still cutting it for these, no less. Dwarf cichlids tend to be quite docile and won't bug your other fish like larger cichlids would.
You could also try some honey or licorice gouramis, or even a betta if you remove the platies. I'd steer clear of dwarf gouramis as they can be a little aggressive and they're prone to diseases.
Don't add any of these fish if you don't rehome some that you've already got, though. Your tank is megastocked for 60 liters.
