My Dad has a Problem and I Need Advice

Hello,
I am a young women and am a full time student in college so I currently live at home with my parents. When I was younger my dad went to a rehab center for alcohol/sex/ porn addiction. I had never seen him drink growing up and truthfully I don't think he had a problem with alcohol but at that time porn addiction was not talked about or well known about. I think that in order to get treatment for addiction he was lumped into sex and alcohol addiction when his real problem was porn.
My dad works from an office at home and spend hours in his office on the computer he will be in there from 6 a.m. tell 6-7p.m. I wasn't worried about it previously because I know he works hard.
Recently I walked into his office like I have done many times before, unannounced to ask him a question about school and I caught him looking at porn. Normally this would just be an awkward situation and nothing to worry about but because of my dads past history I'm concerned.
I have started to notice a change in his mood and behavior that I never noticed before. he spends a lot of time in his office even on the weekends when he's not working, he has become increasing more irritable and hard to be around and he can't go for long periods of time with out needing to go "check something on the computer"
I think this is an issue and should be brought up to him so he can get help again but I'm stuck between a rock and a hard place. This is where I need some advice because I'm not sure what to do.
I would tell my mom but I know she will take it personally and I'm afraid that she will be reactive about it and everything will blow up and become a huge problem. I asked my brother to talk to him about it and he said he would but that was weeks ago and I don't think he has done it yet because today I think I almost walked in on my dad doing it again. I would normally bring it up to my brother again but he's currently in the processes of moving and starting a new job and I don't know when he would be able to talk to our dad. I don't really feel comfortable talking to my dad about this and I wouldn't even know where to start. I love and I care about my dad and I want him to continue to get help, but I am a young women and talking to my dad about this makes me feel uncomfortable.
My dads mood and behavior has become unhealthy and its hard to be in the same house as him. Should I wait until a better time to ask my brother again? Should I talk to my mom? or should I just talk to my dad about it?

 

I'm not sure how I can bring it up! I feel uncomfortable talking about it. Any adive on what I should say or how I should bring it up

 

Thank you for the advice I appreciate the time. I no longer walk in unannounced. I told my mom today and she is going to talk to him about it tomorrow.