Anal gland issues

Hello,

New here to the forums. I have a two year old male pit mix. About a month ago, I noticed he was scooting a lot and he had the typical anal gland fishy smell so I took him to the vet who had to express his anal glands. I started him on a fiber supplement. Now, his stool is soft and he has that odor again. Is there a food that is recommended for dogs with this issue? Should I start feeding him grain free? I switched both of my dogs from grain free to Pro Plan sensitive skin and stomach which is salmon and rice. I've been avoiding grain free foods for my dog due to the FDA saying that peas can cause dilated cardiomyopathy. I just need some guidance if anyone has dealt with this issue. Thank you!