Neon tetra tank mates?!?

85 liters roughly equal to 20 US gallons? With 20 tetras already there not much space left. If you really want to add something add 4-5 corydora catfish they stay mainy on the bottom and do not disturb tetras, you may try getting a dwarf gurami. Shrimps are excelent addition if you have good lid on your tank and your tank have 0 ammonia and 0 nitrites. They are extremely sensitive to it. I love to keep a pair of juvenile angelfish with a school of neons. They look awesome, however you better have separate tank for angels because when they grow up they may consider neons as a tasty snack and they do need lot of space for themselve. (20 gallons) for a pair is good