Very warm water can increase a flowerhorns aggression and stress. That male looks like he is about 3.5 inches. I would let him get bigger before I allow them to be together. You don't want them to fight. Females can lay eggs when they are 2 inches. I have had 3 that laid eggs at 2.0 inches. I was so surprised. But the males need to be 4-5 inches before they will be mature enough to fertilize the eggs.