This condition may be a sign that you may be over feeding your dog...and possibly choosing the wrong kinds of foods. I read somewhere that Acid Reflux can lead to a precancerous conditon, also Acid reflux is often related to respiratory problems like as asthma.
As show pug mentioned feed smaller meals more often throughout the day. The proper amount for the "desired" weight of your dog
staggered throughout the day.
Some suggestions:
Try a bland homemade diet for a little while and read up on allergy diets. You could switch to a bland dog food such as California Natural...keep a journal of how your dog responds to each diet. For example, chicken and turkey based kibbles make my Rottweiler bloat (cause excess gas), I can feed these raw or cooked though. You have already found fish and potato forumla's seem to work for your dog.
Don’t let your dog eat right before bedtime, exercise etc. basically follow the same rules for bloat. If you want to try a natural homeopathic treatment, I found Nux Vomica to be wonderful for treating gas and stomach problems.
Stress and anxiety can make symptoms worse.
Some foods that weaken the esophagel and make symptoms worse are tomatoes, garlic, dairy products and high-fat meals. Wheat and other grains containing gluten (oats, barley and rye) are problems for some
Try adding more fiber, I add ground flax seeds to my dogs meals. You can also try fruits and vegetables.
Make sure your dog is getting regular exercise.
Feed small meals. Large meals increase the upward pressure in the stomach and can cause problems even in Dogs without GERD.
Consider marshmallow root, which soothes inflamed intestines.
Consider slippery elm. It can heal irritated digestive tract tissues.
Avoid antacids, which only mask the symptoms. If you must use antacids, avoid those containing aluminum.
Consider giving probiotics with meals. These products contain "friendly" bacteria that can stabilize the digestive tract.
Make sure to discuss supplements with your Vet to ensure they won't interact with any thing your dog may currently be taking.
I didn't read this article, but usually the Great Dane lady has some great advise. Here is a link and view the whole site for some great ideas.
http://www.greatdanelady.com/articles/feed_program_for_program_for_sensitive_stomachs.htm