When was your cat last dewormed? It may be a good idea to take him and a fecal sample to your vet to have it checked. If you have a good relationship with your vet he may take a fecal without you having to take the kitty in for a checkup.
Have there been any other changes in his diet? IE: letting him drink cows milk, plants he may have munched on that may be poisonous, anything unusual.
Please DO consider changing his diet. The runs may be
diet related. There are much better quality canned foods out there. You could even consider feeding raw which is the best you can do for your cat's health. Drop the dry food all together. Especially when you have a male cat. Cats need their fluids with their foods. Not beside it. I will give you a great website to check out. The information included in it is priceless. www.catinfo.org
Good luck with your kitty. Let us know how he is doing.