I'm not very familiar with how hole in the head begins, so there is a chance I am wrong on this.
Ok, now that i put up that disclaimer, i am thinking maybe he is seeing his reflection and charging the glass out of agression issues? I know red devils live up to their name, so he could possibly think there is another fish? Kinda like bettas and how they go after mirrors.
Since you are concerned about hole in the head beginning, i know that alot of it stems from fish who have not had proper nutrition, so make sure he is getting a varied diet, and living off of more than feeder fish.
Here is some more info for you. I am not the writer of this information
About Hole-in-the-Head Disease
Drs. Foster & Smith Educational Staff
Tiger Oscar
Although the name may sound humorous, the disease is serious. Primarily affecting cichlids and also known as Head and Lateral Line Erosion (HLLE) or Hexamitiasis, this condition is still poorly understood. Many believe the causes are poor water quality and a lack of vitamins A and C. In most cases, the etiology (cause) is probably an internal normally harmless parasite, Hexamita, which lives in the fish's stomach. The hallmark of this disease is erosion of the pores along the front and side of the head. This does not always happen and many authorities believe almost all aquarium cichlids are affected to some degree with Hexamitiasis and readily transmit the disease to each other.
It is believed that when the cichlids are stressed and weakened from vitamin deficiencies, poor quality food, and/or poor water quality or other stressors, the Hexamita migrate through the fish's system. The sensory pores (on the front and the side of the head) become pus-filled if the microbes migrate to these locations. If the parasite invades a vital organ, death follows. Since the fish's immune system is already compromised by the Hexamitiasis, serious illness may also result from the secondary invasion of bacteria or other parasites.
Treatment is only conditionally effective using metronidazole. It is very important to treat all cichlids from an infected aquarium whether or not all are showing outwards signs or symptoms. Choose a medication such as Hex-A-Vital or Hole-N-Head Guard. Follow label directions carefully and provide fish with a stress-free environment, high quality food, and vitamin supplementation, including B-Complex, to help increase the fishes' appetites.
