totally normal activity. i will warn you mocha are VERY aggressive... my female used to drag the male around the tank when she's ticked or its feeding time. it could also be that your bigger one was a male in the store and is still changing sexes.
my clowns are siblings. had them for 2.5 months before who got to make the sex change decision and really did a job hammering. I have the video but don't YouTube host. the addition of other fish also changed behaviors. a dotty became boss chasing the clowns, then a jawfish stopped the dotty chasing. a couple damsels and we are all happy campers. till I stick my hand in the tank and the jawfish tries to bite me now. and now the missing link re-appears trying to pinch me. a 2.5" emerald. the bubble algae must have had prednisone in it.
