I have the same issue between my GSD and one of my huskies. They will be chasing each other around and playing one minute and the next they are on top of each other fighting. The fighting isn't too serious as I can stop them with a loud, sharp NO! but my GSD and my lab on the other hand get really serious when they fight. I have to physically break up their fights every time it happens.( It doesn't happen very often though) What I usually do is I pull a tail of a dog then I will hook my arm under the front of their back legs and pull. Or if one dog is on top of another then I, with my whole body, push the dog off of the other dog.
These are more dangerous methods as you have to get physically involved which possibly means getting bit so I usually first try a non physical method before I break the fight up myself.
Using a hose only works if the hose is right there and turned on where ever there is a fight. I have had situations though where the hose was handy and it did work very well. Its just a matter of where the hose is and where the fight takes place.
Another thing you can try is take an empty pop can and fill it with pennies or something similar and tape the opening so they don't fall out. When the dogs start to fight, shake the can at them to distract them. This is also a matter of if there is a pop can handy where the fight takes place so you might want to make up a few of these cans and put them in the places that you frequent the most.
I know it is a little different with Pitbulls than it is with other breeds but this is what I do with my dogs. I hope this helps!! (I hope it makes sense too..lol)