i had this problem;
I was using the 'original vitalin', the one which is still yellow when you add hot water, but i switched to the 'gravy vitalin' which is a red colour when it's wet. I think the added flvour of gravy was enough to turn the carp on but i also add, chopped and whole boilies, different sized halibut pellets (3mm to 14mm), tuna chunks, sweetcorn, hemp and some liquid attractant. It may seem liike a witches potion, but i know by trial and error, that on my local lake, it works!