hey there
christine, i'd suspect your fish are fighting. a lot of times fish become stressed out in dealer tanks and therefore are less active, les defensive. or, maybe the fish on the other side had a dominate male and these 2 were doing their best to stay away from harms way. either way, my bet is you have 2 males and the new home envoked a fight for territory to establish the dominate male. they won't always chase each other, but a dominate one will certainly be established. the other will remain hiding most of the day. worst case scenerio, one male will kill the other male. if fighting continues, you'd be best to remove one male unless the system is large and contains lot's of LR. if it is a female, it will be right at the side of the male.
unless one is carrying eggs, IMO it is impossible to tell the differences in sexes. also, a male with repeated hatches tends to keep it's swelled jaws between breeding attempts. there are some articles out there that claim of ways to tell the differences of sex, but after using them i was left even more confused. quite simply, i don't think there is an easier of sexing your fish other than a pregnancy or autopsy.
chasing is something left up to fish that are defending their territories. a male banggai will not defend it's territory against females - only other males. that being said, the mating ritual that takes place has one banggai dancing infront of the other. from left to right, the male vibrates - think of a pager going off on vibration mode - intensely, spending no more than 5 seconds on one side before moving to the other. the eggs are dropped on the substrate, the male fertilizes them, and then
promptly scoops them up.
i think it would be in your best interest, if you plan to raise baby banggai, to remove them from the main system. feeding baby banggais can be difficult, and having them as part of a larger system makes it tougher. i've had good success removing them and placing them into a 5g tank with LR and LS. since doing this, i've had a higher success rate of raising them. i don't know if it's from natural food, or natural protection, but i've definately had better success with the LS and LS vs a glass bottom. also, i've had better success at getting the fry when i caught the male with the brood still in his mouth. it was very difficult to catch the fry in the system without the other fish and coral getting a couple. also, waiting all night long sucked as well. instead, i catch the male once i see the fry peeking out of his mouth. i know they are ready, so i net the male. once net, the male promptly spits out all of the fry. he makes it really easy for you. of course, you've got systems already started for both the fry and the male to recooperate seperately.
lastly, i'm not calling anybody a liar, but i certainly would have to see the gentleman raising fry in his overflow before i'd believe it. IMO and IME, there is no way that is possible. again, JMO.
HTH
henry