I am a beginner and have a 15 gallon high tank(20"x10"x18") with plants like dwarf hair grass, anubias nana petite, ludwigia super red, Bacopa caroliniana & a few water lettuce. There are 6 widow tetras, 5 cherry shrimps & 1 spotted nerite snail. They have all been doing fine for about a month now. I really would like to add some chilli rasboras. Is it possible? If so, how many should I add? Please point out mistakes & give suggestions since I m new to fish keeping.