I'm surprised that he wasn't placed on Lasix first, rather than Aldactone (a mild diuretic with potassium sparing properties) alone. However, since he's had the TIPS, they probably wanted to give him the least diuretic as possible. It seems to take awhile to get off diuretics after TIPS.
As to the weight gain, I really don't know. Has his appetite increased? As Rick mentioned, he needs to watch his sodium intake closely.
Hugs,
Connie