Sorry if this post is long. But let me give a quick background before I get into the main story. BACKGROUND: Ok so I have owned rats in the past and have never had problems with aggression. So I decided to get a new baby about a month ago after not owning rats for a couple years. My plan was to get two but they only had one boy left. I could not just leave after I saw him so of course i got him. His name is Roger and he is an Albino. About two weeks later, they finally got more rats ready to be taken home so I went to get a new friend for Roger. They only had 3 rats. Two of which were in one cage and the other by himself. I could never separate the two who were defiantly liter mates so I chose the one by himself, which I named Derp. Derp is much larger than Roger or any other rat that is supposedly 6 months old. He is the biggest rat I have ever owned, which made me feel like he might have been older than claimed..but who knows..anyways.. Roger and Derp got along instantly. Roger is very laid back were as Derp is very brave and hyper. They compliment each other...I could tell Roger was much happier with him. So all has been well, I take them out daily and have been making great progress with trust training etc. I was never bitten and they stopped leaving droppings when I took them out. .. Watching Derp run around made me want to expand their home. So I built a two level topper. Instantly Derp ran up the ramp and loved it!! I was so happy. Roger however did not even try to go up there which I figured maybe he was scared. Well the other day he finally went up there and then everything went south. My boys didn't fight but Derp started running up and down from the bottom all the way to the top...which was making Roger scared..too scared to move and get back down to the bottom level. I took Roger out and cuddled him for a bit and put him in his favorite tube. I thought all Was well since Derp had calmed. Few hours later I went into the cage to change the water and clean the liter pan when Derp came running and nipped my finger, not hard though. Okay I thought...he had never done that before. I finished cleaning and went to pick up Derp for our nightly out of cage bonding..well he bit me..hard and broke the skin. Shocked and upset I closed the door and went to wash the wound. I came back and he's stuffing fluff infront of the door almost like he does not want me to go in. I let him be for a little while thinking maybe I startled him when I tried to pick him up. Well I had an almond for me and put my hand back in the cage. He smelt the treat and then violently bit my finger, purposely!. At that point I went back and washed off the wound. I came back to him running around between the two levels of the topper when Roger decides to go sit on the lower ramp. Derp charges at him and mounts him. Violently. Roger was so scared he wouldn't move! Now I can't even open the cage door or else Derp will try and attack. I cant get to Roger and I can't clean the cage or anything. He has not attacked Roger only mounted him. But he no longer cuddles him. I have no clue what to do. I have never seen this happen before. I am very worried as It might cause Rogers myco to flare up if he's stressed. This is the first night i have not been able to touch them, take them out, and clean the cage. I'm guessing its a territorial thing going on. Probably hormones acting on it too ( both are not neutered). I cant even take the topper off without having to go in the cage...but he is right by the door waiting anyways. I have also noticed Derp: Drinking alot which may be from him running and jumping around, excessive sniffing when I'm near, and not giving Roger any attention..he rather sleep on the top floor of the cage topper then cuddle with Roger in their tube. What can I do! ? I don't want to return him. I'm not sure were around me will neuter a rat and how much that would even cost. Thank you so much for any help!!!!!