Recently, I have been doing sessions to better capture the color profiles of Dawn Pro and other detergents at various dilutions in order to come to a better understanding of them. Bubble colors tell us about the thickness of the soap film which in turn tells us about the surface tension of the solution and the strength of the surfactant.
Most of the recipes on the wiki assume that a detergent with similar qualities to Dawn Pro is being used. Most versions of Fairy and Dawn Ultra are similar to Dawn Pro in terms of surfactant strength. In years past, there was a product call Dawn Non-Ultra that was a favorite of bubblers. Currently, there is something called Non-Concentrated Dawn or Dawn Simply Clean, and people periodically report that it does not work well for them.
I picked some up and have included it in my color profiles project. From looking at the bubbles created with Dawn Simply Clean, it looks like the surfactant strength is about half or a bit less than Dawn Pro's. Below is a Dawn SimplyClean solution at 11:1 compared to Dawn Pro at 20:1.
NOTE (Nov. 2018): It is worth noting that Dawn Simply Clean seems to be inferior to other Dawn's even when you account for its lower concentration. Quite a few people have reported over the years with Dawn Simply Clean and its predecessor Non-Concentrated Dawn that bubble juice made with it simply doesn't work as well as that made with the full-strength versions of Dawn even after you adjust for the lower concentration.
I also look at how much acid it takes to neutralize a 10% detergent solution. It took a bit more than twice as much acid to neutralize a 10% Dawn Pro solution as it did to neutralize the Dawn SimplyClean solution. While such a test would certainly wouldn't be valid when comparing unrelated detergents, in this case, I think it is an indication of the relative strengths of the these detergents. The 10% Dawn Simply Clean solution had a pH of 9.01 while the Dawn Pro solution had a pH of 9.1. Both were made with distilled water.