Just put it in however deep you want it in your tank. My Ph runs 7.2 -7.4 and the fish are fine. So your 7.7 as long as it stays pretty well steady is ok.
There is no way to compare what happens in the wild in lakes and rivers with our enclosed aquariums. Because of the small ecosystems we try to keep our fish in we have to be more careful to keep the parameters good and the Ph stable. In the wild if they are uncomfortable they can swim away and find what they need. In the aquarium they are stuck with what they have. Thats where we as fishkeepers come in

Carol