[rayjay]

First of all stability of the salinity is NOT a cause for gas bubble disease.
Small bubbles in the water are also not responsible.
Most likely cause is chemical imbalance that may happen from water that hasn't had sufficient tank husbandry.
NEVER massage air from a pouch. Instead, use a cannula or rubber tipped bobby pin and open the pouch while the seahorse is upright and under water.
You have only mentioned the pouch as "inflated" and haven't mentioned a buoyancy problem. That tells me you don't have gas in the pouch as it would probably be tail up or at least floating on it's side and having problems staying down in the tank.
Males inflate their pouches as a part of courtship to entice the female to produce eggs for him to accept.
It's also a possibility that the seahorse is pregnant.
Many males tend to be less active than the females. (but not all)