Zebra Danio Behavior

Question
I recently got a secondhand tank with two Zebra Danio in it.   I've never had these fish before, so my experience with them is basically nothing.  Lately, one has been chasing the other relentlessly near the surface.  Is this a breeding thing?  Should I isolate them?  If they breed, will their angelfish tankmates eat the eggs and fry?  Oh, they are about an inch long, one is more of a silver striped, the other is a coppery gold.  The tank I have is 20ish gallons, with a heater and canister filter, and several live and plastic plants.

Answer
It could be a breeding behavior however it sounds more like a bullying behavior. I suggest taking out the aggressor as it is stressing your other Danio and placing it in another tank. If they do breed then yes the angelfish will eat the eggs and fry. From the size you tell me and the color coronation they seem to be around the adult age but not exactly an adult. If this behavior continues then you risk the chance of losing your Danio who is being pacifist.