sorry i would suggest moving them to a bigger tank so they don’t kill each other , my research into this fish which has been the only fish i have researched until late suggests that 15 gallons min for one of these alone and 25 gallons min for 2 or they are going to nip or kill each other.
mine are social to each other in 30 although feeding time is very unique having to bring food to each of them with tweezers at the levels they are currently at , or they will go after each other for food.
sorry for worrying but 7 gallons seems way to small even to keep them for a short time