In my experience, Simple Green doesn't work well if your chain is very dirty. I use the stuff by the gallon, but I've found that even after I clean the chain with the Simple Green and it LOOKS clean, if I then do an additional cleaning with a citrus based solvent such as Pedros, a lot more grime comes out in the Pedros, i.e. the Pedros turns black. My solution has been to use several cleanings with Simple Green as a preliminary solution to get the visible mud and gunk off and then do a final clean with citrus solvent. I've also found that the bike-specific citrus chain cleaners work way better than what you can buy in bulk at the hardware store. I don't know why; the bike-specific cleaners just work better. No matter what water soluble solvent you use, it is very important to rinse well with water when you are done to get all the solvent out. Then when the chain is dry, be sure to carefully re-lubricate each and every chain link.