The powders have been having trouble since the switch from phosphates. There was an article in Chemical and Engineering News a couple weeks ago (I’d link, but it’s paywall, so unless you know someone who’s an ACS member you’re out of luck.) The gels tend to have the same problems. I will post a couple quotes from the article.
“For an idea of what people are thinking, take a look at the website for Procter & Gamble’s Cascade, by far the leading brand name in U.S. ADW detergents. P&G’s high-end single-dose tablets continue to garner good reviews. But the firm’s workhorse ADW powders and gels are getting slammed. Comment pages that a year ago were filled with praise for Cascade’s effectiveness now brim with invective from unsatisfied users.”
“P&G consumer care representatives bravely respond to many of the angry posts. Often they note that, because Cascade products are now phosphate-free, consumers who live in areas with hard water might experience filming or spotting on their dishes. They suggest that dissatisfied customers try one of the single-dose products.”
“Product form is also important. Quantum tablets contain three chambers separated with dissolvable polyvinyl alcohol film. According to Magg, the chambers isolate incompatible ingredients and then control their release in the dishwasher. For example, Quantum’s center chamber opens later than the others to release ingredients that help prevent calcium deposition, he adds.”
There’s also a lot of technical talk and I’m afraid that quoting too much more will run afoul of the board’s IP policies. Basically, the loss of phosphates has caused many problems with formulation, as the phosphates made it a lot easier. The various manufacturers are currently looking at a variety of different solutions, including enzymes, biopolymers, chelators, surfactants, new stuff being released by BASF and AzkoNobel, and so on.
Personally, I suggest buying a box of tablets. I prefer Finish Quantum, made by Reckitt Benckiser (a European company), which cleans quite well and is fairly cheap, especially as they often have pretty good coupons in the paper. If you prefer Cascade, try a box of Cascade Complete tablets. I see that the gelpacs have also been recommended.
Another thing to check might be the water temperature. I found that I was actually running the water too hot at first, and when I took it off the pots and pans cycle and put it back on normal the detergent actually worked better.