This is rather a complicated issue, and as you indicate you are new to the hobby, I will take the time to explain it. We are dealing with a totally scientific hobby, meaning that the processes of the natural world are involved, and it is not always easy to understand these at first.
Shoaling fish species, which includes all characins (tetras, hatchetfish, pencilfish), cyprinids (loaches, barbs, rasboras, danios), rainbowfish, and many "catfish" (corydoras, etc) must be in a group. Many people have a smaller rather than large aquarium so "minimum" numbers are asked for and become somewhat standard. But this is not really being fair to the fish. The more there are in the group, the better, with very few exceptions.
When a shoaling species fish finds itself in less than expected surroundings, as here with only four of them, it will be stressed. The effects of stress on fish are very complicated physiologically, and are often subtle. There may or may not be external signs discernible to us—it can continue for weeks and even months, sometimes up to the point when the fish just suddenly dies. The reasons for this are involved, but to avoid a book length post I will move on but can provide more info if asked.
Short-term stress will cause an increase in heart rate, blood pressure, and respiration. The fish can only maintain these altered states for a short and finite period of time before they will either adapt or (more often) the stress will become chronic. During this initial stage the fish may look and act relatively normal, but it is depleting energy reserves because of the extra physiological requirements placed upon it. At the chronic stage the hormone cortisol is released, which is responsible for many of the negative health effects associated with stress. It is common in many species for the fish to resort to increased aggressive behaviour as a means of dealing with the frustration stress causes. That is what you are seeing here.
Increasing the group might or might not solve this problem. Once fish are stressed to the point of changing behaviour (for the worse usually) it is not going to return to normal because the damage from the chronic stress cannot be undone. You could try adding another five or six (a group of 9-10 or more is advisable as you have the space) but it may as someone mentioned continue or get worse. Eventually the aggression will likely be directed to other species. Removing the four Glo Tetras might be the best solution. But this is your decision, I can only explain the problem.
While I'm here, there is another problem pending, with the Bala Sharks. This species, Balantiocheilos melanopterus, is obviously not a true "shark," it is a barb. This is thus another shoaling species, and here it is crucial to have more of them right from the start. This is a shoaling species with a pronounced social structure within the group, and it must be maintained in groups of at least five fish. Fewer will result in aggression to the point of death of subordinate fish, and/or aggression toward other species in the tank. When it says "at least," it is always better to have more. However, the tank space is going to become problematical very soon as these fish grow. Fish grow continually, and must have the necessary space throughout. Moving them to the larger tank, which must be 8 feet in length (this fish attains 14 inches, some report up to 16 inches, and it is an active swimmer), within a matter of weeks is crucial for their continued health. It is also not a true community fish, so that's another issue.
I definitely wanted to add some live plants at some point and I don’t keep the light on them 24/7. I like to try to condition them to a natural daytime/nighttime routine as they would experience in the wild.
