i have a 20 ga tank. it is currently cycling (fishless) i am starting to plan out what i want to stock it with. i really like the red-tail shark or the rainbow shark. this is what i was thinking 1 shark, 6 schooling fish (lemon or black skirt tetra), 4 corydoras. is this doable this is my first tank. i really want the shark so if u have any sugestions to go with the shark it would be greatly apreaciated.