Actually, that brings up other questions/concerns
I see in that tank one(?) Angelfish, and three Neon Tetras. There is more, but they were hiding, not sure if they are more angels or something else.
I also saw that this is a 65L aquarium, which is about 17 gallons.
Both Scalare Angelfish and Neon Tetra are schooling fish, which means they like to be in a group of their own species, the absolute minimum for Scalare Angelfish is 4, but 5+ is better. For Neon Tetra you need at least 6.
However, this brings up a couple issues. The first being that these two fish are not compatible, the Neon Tetra are a natural food for Scalare Angelfish and once they get big enough for the tetras to fit in their mouth, they will eat them. The same goes for any small torpedo shaped fish. This brings up the second issue, Scalare Angelfish get fairly large at 6" (15 cm) in length. Due to needing to keep these in a school, and their large size, a 55 gallon (208 liter) aquarium is the minimum size for a school.
However, that said, it is possible to keep just two angels in a smaller aquarium (30+ gallon) if they are acquired as a mated pair.
You can click on the shaded names for the Scalare Angelfish and Neon Tetra to read their profiles and get additional information on their care and natural environments. I would suggest either finding a good home for the Angelfish, or acquiring a larger aquarium and fleshing out their school (although this can be problematic when all the angels are not acquired together. They are still young, so it may work out well).
You'll want to come up with a solution relatively soon, as growing up in too cramped of an environment will have negative long term health affects. Fish grow very quickly.