How many shrimp can I have in a 5gal?

I have densely planted, cycled, Fluval Spec 5 that has been running for about 3months with 20 Red cherry shrimp. I do a 15%water change weekly and they seem happy and healthy. I would like to add some other color varieties of Neocaridina davidi. What is the max# of shrimp I could add?