Need help with introducing some guinea pigs?

Valid point, Lonin, but I wouldn't say the "falling out" between pairs is so devastating. As long as there is no serious fighting, any kind of mounting or dominance play is normal and healthy for them to express. Even if things aren't quite as peaceful as before, it's just a matter of time before the new group settles their differences and begins to get along on a whole new dynamic. I would never discourage someone from adding a third piggy, but that's me.

If you are going to try introducing, make sure it is stretched over the span of a week, with daily neutral territory meetings. Good luck!

Mounting is completely normal and harmless dominance behaviour, he wasn't in pain. There's no need to separate over it.

But if they're all males and your pair already get along with no problems it might not be the best idea to introduce another. Trios or larger groups of males often don't work and can even cause the pair you have to fall out as well. If you did decide to attempt it, 3 males would need an absolute minimum cage size of 13sq ft.

http://cavyspirit.com/sociallife.htm#Introductions or http://www.theguineapigforum.co.uk/showthread.php?... for introducing guinea pigs :)