Aggression of clowns after 1 year

[Ziva]

Hello. I've had 2 Percs for exactly 1 year today. They were purchased together and are the only fish in the tank .They were both scarcely 3/4 " the one only slightly larger. They are the only fish in a 30 gallon tank. My water perimeters are perfect and have never changed. No nitrates No phosphate. I've noticed that suddenly the one I assumed was the male -only because it up till now was noticbly smaller than the "female" has grown almost overnight and caught up to "the female" in size. They aren't fighting exactly but have been slightly agitated, either toward each other or perhaps they've noticed their own reflection on one side of the tank. The only recent addition to the tank is an AP700 fixture which has changed the whole look of the tank. Could any of these factors caused the change in my fish or are the becoming sexually mature ? Thank you