Males chase females to mate, but as long as you have three to five females for every male they should be fine as he'll soon get distracted and move on to another female, leaving each alone for a while at a time.
Females chase males to either tell them they want to mate or tell them to get lost of they're sick of the male chasing them around. If a female is seeming to taunt the male, maybe 'fluttering' her tail of swimming up to him and then swimming off again then this is flirting. She want's to mate with him. If she's chasing and nudging him, maybe trying to nip then she's telling him to get lost 'cause she's sick of him!
Males chase other males to determine dominance. Just as with other Animals a pecking order needs to be made and this this is then constantly kept in check by reminding all as to who is where in that order. But again as long as they all have their own little group of girls them all should stay safe. If not they will fight for the girls and this can lead to deaths.
Females chase other females to determine dominance too. Just the same as the males, but they tend to be a bit less rough. But this shouldn't cause a problem.
As long as you have enough females to each male then things shouldn't get out of hand. They do tend to chase eachother round a lot and some of it is playing with the rest just being either a dominance thing or just a breif squabble. Just like kids do really.
If your males are chasing eachother and nipping, causeing damage, then that is fighting and could end badly if not sorted out. But if they're just nudging eachother, pushing eachother around, shoving them out of the way etc then this is pretty normal 'lads' behaviour.
The same aplies with a female chasing a male. As long as their is no damage being caused then all should be fine... as long as he gets the message.
Make sure you have plenty of hidey places and plants for them to get away and hide for a while, give themselves a break if they're being pestered. And just keep an eye on them. Normaly they can look after them selves as long as their numbers are well balanced. If everyone is eating and swimming around quite happily with everyone else, not hiding or their fins back and down, then they should be OK : )
