I turned on my light this morning to see 3-4 of my black skirt tetras chasing(?) a blue skirt tetra. The black seem to have a new red streak down spine area as if they’ve been scratched? Are they bullying? Mating? Never had this problem before should I separate the blue fish?? They kinda seem to get up under but the blues seem stressed. The black skirts are doing this to BOTH my 2 blues actually!! Help!!