@oogabooga without seeing the aquarium, I can tell you that most fish prefer cover whether it be plants, driftwood, floating plants, etc. Without this, most fish will get stressed. Stress can lead to illness. I’d suggest posting a photo of the aquarium and have some of the good people here toss you some ideas. It definitely can’t hurt and notice I addressed it as most fish. There are certain basic rules that come with a bit of experience. One of those being, fish like to feel safe. Also if they are the only fish in the tank, then there’s no other fish to sort of set the mood. 4 is also not an ideal number for a shoaling species, so without knowing the size of the tank, I’d say you should add at least 2-4 more. Good luck