You should increase the water level to almost to the top maybe about 3 inches lower then the top glass. Having a tank with too low water level will speed up dirt and bacteria in the water and it greatly reduces the amount of movement fish should be having. If you are going to put more water in the tank do so very slowly. Pour the water in a part of the tank where there are no fish. Pouring the water in the tank should be done slowly mainly to stop the dirt from the bottom of the tank making a mess. If the water does get dirty due to pouring the water don't worry it will settle. Other then that good luck with your new fish and i'm sure they will live for a long time. Just one other thing, don't over feed your fish! It's the most common mistake lots of people make. I would recommend you feed them once a day only a small pinch. Good luck.
10 years of keeping tropical fish