Might not be the Tetra's that kicked off the issues, could have been the Guppies...even single sex Guppies have a pecking order...
TBH every aquarium has a pecking order....there will always be a top dog and their will always be at least one or two who are maybe smaller, more timid, harbouring birth defect/illness that the other fish in the aquarium will pick up on and take advantage of
Fish can be absolute thugs when they want to be. Fish like CAE and Betta are genetically wired thugs and you can see trouble coming.....but other species, not so easy to spot the thug in the pack but you soon discover who are the weaker ones cos they always seem to pick up injuries, be afraid or stressed or not eat well
