I haven't personally kept those, but I have a lot of wild caught CPD's, so they should be similar. My CPD's will eat anything I give em.
Wild caught fish can take some time before they accept commercial foods, plus if that is a new brand food to them, they can take days before they accept the new food (pretty much have to starve before accepting new foods, which is common among fish).
So I'd say, just keep feeding the foods. If those are .5mm pellets, they should float for a while if placed gently on the water surface. If you have a ton of rapid current, then turn off the filters for a bit or feed directly where the fish are if the pellets are getting kicked down fast (they do sink fairly slowly).
Flakes tend to sink slower than pellets, and they scatter better so it reaches the fish better.
In the mean time, if you are worried about them starving to death (you do want to starve them to ween them onto new foods, but just recommending frozen or live if the fish is dangerously skinny), frozen bloodworms seems to be a favorite among most fish. Feed that every so often, but still feed the commercial dry foods as well, so they get accustomed to it and not get spoiled on frozen or live foods. Live foods are another option you could do until you ween them onto a commercial diet.