So much craziness in this thread.
One: You do NOT need a sump for a tank that size, that's nuts. A good hang on the back filter like an aquaclear will do just fine. I see you have one on there, hopefully it's a good one and not one where its a simple cartidge you change out weekly when it gets dirty restarting the "cycle" every time.
Two: Did you cycle the tank? If not go buy some "cycle starter" like API quick start or Dr. TIm's, it will jump start your cycle (aka nitrogen cycle)
Three: 4 RBP in a 10 gallon will not work, probably not even short term, they are VERY cannibalistic at that age and you will most likely only end up with one or two at the most. You should start with a small shoal of them in a much larger tank to give them room to "flex" so to speak.
Four: They are also VERY skittish fish, they WILL hide....a lot. Especially when not in a shoal. I've kept as many as 30 at once and they never hid, I've also kept as few as 10 and they were skittish and bounced off the walls at the slightest disturbance. Maybe some taller bushy plants will help them feel more secure, but I would not expect them to come out and say hi
Good luck, but I think you have made a poor selection in species for that tank unless you plan to rehome them soon.