I'm going to guess that either the betta you lost was either ill when you got it, already significantly stress and when you added him to the tank with an ammonia of 6 - 7 (I think that's what you had on 6/26) it was just too much for him.
BTW I have 2 male bettas, each is in a 2.5 gal hex that have UGF. The airstones in the airlift tubes cause some surface agitation - but not enough to even make their fins move. I even have tiny heaters in these tanks to keep the water around 75F. I vacuum the gravel and perform water changes about every 10 days. They appear very healthy and happy.
Some folks think that because bettas in the wild are found in shallow, stagnant puddles - that is how they should be maintained in an artificial environment like an aquarium. IMHO, the bettas you get from breeders and the LFS are most certainly not wild. They have been specifically bred to have the characteristics that humans desire, not what is best for the fish. You wouldn't expect a AKC pure bred tea cup poodle to thrive in the same environment as a pack of dingoes, why should the betta?
This post is most likely to get heavy critisism - but the above is mearly my opinion. Like particular body parts, everyone has one.