76 degrees is slightly cool. Can you raise the temp a bit?
Has he pooped at all lately? If so, what did it look like? It should be red/brown. (If it's white, that could indicate an issue such as internal parasites.)
Aquarium salt is the wrong salt to use for issues like constipation and bloating. The rule of thumb is:
- Epsom salt for internal issues (constipation, bloating, etc)
- Aquarium salt for external issues (fin rot, etc)
I recommend discontinuing the Aquarium salt, and buying some Epsom salt instead. It should be 100% pure magnesium sulfate. (No dyes, perfumes or additives.) It's available at grocery stores, drug stores, Walmart/Target, etc.), and it's not expensive. It acts as a laxative (in people too).
Also, I'd suggest not feeding him for a day or two. One or two days without food shouldn't be a problem for him. And the Epsom salt should help relieve any internal bloating, if there is any.
I also don't recommend a pea, personally. There's a lot of controversy about whether using it for bettas. Plus, the Epsom salt will already act as a laxative.