Carbs. Dry foods are much higher in carbs than canned foods, sometimes as much as 40% for a really poor quality grain and filler filled brand. There is one brand of food that supposedly has no carbs at all but that's debatable. Dry food needs something starchy (a carb source) to hold all the ingredients in that nice kibble shape.
You can put all the essential vitamins and minerals in a really poor quality dry food and it will meet a cat's nutrient requirements. All pet foods in the US that are labeled as a complete diet are required to meet minimum AAFCO nutrition requirements.
Catinfo.org is a good place to learn more about proper nutrition and why dry food (in a perfect world) should not be fed. Some people do feed only dry food for various reasons and should not feel like a horribe pet owner because of it.
All of those reasons! Not all dry has carbs or bad ingredients, though. I think it's mostly because of the lack of water though, since cats don't really drink water since they're used to getting it from their prey.
There is a brand of dry food called Young Again that claims to have no carbs.
I'm not sure how many carbs are in Acana. The only dry food chart that I know of that has carbs included is several years old and has not been udpated since so many of the newer brands of foods are not listed. It's probably safe to say that many dry foods, even grain-free ones, have too many carbs for cats. Ideally carbs should be no more than 10% to 15% of the diet. A small amount of dry food in the diet would be ok. Y ou could balance it out with some low carb canned foods. Some canned foods have no carbs at all.
Seafood based foods in jelly / aspic tend to be the ones with no carbs.
Oh, carbs can come from veggies and fruit, too, not just from grains. So a grain-free brand of food (dry or canned) that contans fruits and veggies may still be on the high side of carbs.
I have always fed a good quality dry cat food to my cats. I have had multiple cats who have had problems eating fish so I always make sure there is no fish of any kind in any of the food I feed them. I added a link about fish and cats but there is a lot more research out there about it. I suggest for kitty sake you might want to research a little more about fish and the problems cats have with it and decide for yourself. I for one never feed fish to my cats. http://www.catster.com/lifestyle/is-fish-in-cat-food-bad-for-cats-maybe-more-than-you-think