new fish tank

I recently got a 20 gallon fish tank and I've done the set up. The pet store told me to fill it with regular tap water than add the de-chlorinating stuff and let it run for a week. I've also in the beginning washed down the tank and all the decorations/rocks with cold water. I had my water...

I have just bought a new 20l tank and set it up for tropical fish. With gravel, filter, heater and plant etc it has 14l of water in it. I bought a small angel fish, sunset colored platy, Congo tetra and tiny bristlenose. The guy at the aquarium shop told me he's quite sure they are all female...