I can only list things that have helped me:
Making sure my sleep, exercise and nutrition was good. I found this helped reduce the intensity of negative emotions that would loop into social media.
I use supplements for Vitamin D and Fish oil. These seem to improve my concentration, though it could well be a placebo.
Using a timer for work. I set a timer and work 15 minutes and then take a 3 minute break. In my breaks I stand up, walk around, go into the other room. I try to avoid checking reddit etc in the same place as where I work. If I'm on a break with the timer then I will check it in the next room. I want to build an association of place and activity.
I use blocking tools, but they are just to remind you when you forget. Blocking tools are not a replacement for willpower. The seatbelt doesn't drive the car.
Keep a notebook and write in it before and after work. Try to predict things that will cause you distraction and avoid them or deal with them before it's a problem. At the end of the day, reflect on whether your strategies worked. If they did, keep doing them, if they didn't, try something else. When you start to understand your patterns of addiction you can work out better and more personal ways to deal with it.
Plan for the relapse. It will happen. That's ok, but what are you going to do after?
I hope some of this can help you.
On a related note, I once read a very powerful post about the illusion of knowledge which Reddit gives you, but I cannot find it. If this rings a bell with anyone ...
Maybe a tool such as Self Control (Mac) can help you. It blocks websites for a certain amount of time without a possibility to unblock.
EDIT: The idea behind this being that perhaps the addiction is a symptom of some other problem and trying to get to the root of the matter might help make it easier to find a way around it.
Uninstall Reddit clients on all but a single, non-mobile device.
When you stray off the path, don't beat yourself up, and immediately get back onto the path.
Probably not the healthy move you're looking for, but maybe you can find something healthier that works for you to get addicted to instead.