Hi there. You can actually find this information easily on the internet, you just have to search for it. By the way, I am using the cleaning services like this one leedswindowcleaningservices pretty often, and I can say that these guys are doing their job very well. I don't know what detergent...
There is no detergent that would change the situation very much if the there is no enought pressure from the machi. I suggest you not playing with the chemicals and buy a stronger pressure washer. Sell your`s may be someone would buy it. Better read this to choose a good one...