Max allowed number of same pokemon in a gym.

I was just training at a gym and about to add a gyarados to it, but when trying to add him, he wasn't appearing when I tapped on the "add" button and it was having me select my pokemon. I double checked to make sure I revived and healed him and he was 100% healed. My only guess was that the gym already had enough gyarados, which at this point had 5, so I couldn't add more. Can anyone else confirm this whether it was a bug on my end or if there is now only a specific amount of one pokemon allowed in a gym?

EDIT: Sorry guys, due to user error this doesn't appear to be the case. My stupid self didn't know I couldn't add my buddy to a gym :( Please move along.