Well, Cchung, I sure hope ya don't ever get a Dwarf Lion because it sure wouldn't last with you. A 29 gallon? C'mon, that is pretty bad. Actually, Dwarf Lions need at least a 45 gallon to live in and to thrive and look healthy you will need a 55 gallon or higher. I have mine in a 70 gallon right now. Dwarf Lions can reach a length of 8 inches. Which is relatively small for lions. So, I think a 50 gallon would be the bare minimum for the Dwarf Lion. I would recommend at least a 75 for the Lion and the trigger.
do you have a tank yet? a dwarf can stay in a pretty small tank (20 gallon) and it would take some time for it to outgrow it. but it would have to be alone in that tank and how fun would that be? none. put it in a tank with some other fish in a much larger tank.
I have a 35 right now, but the current inhabitants would be eaten by a lion or trigger. I have lots of shrimp, crabs, snails, a purple loster, and a feather duster that would be a nice snack for these guys. Ijust wanted to know how big I would need to go if I got one of these. I like both of these types of fish.
Landmeier, if you wanted a dwarf lion and a trigger then you would need at least a 55gal. That is if you got one of the smaller triggers. Some get rather large and would need at least a 75 gal. Even then if full grown may need a 100gal. Anyways, a smaller type trigger such as a picasso,bursa, or crosshatch and a dwarf lion would fit in a 55gal together. Any mixture but no more than two I'd say. Perhaps three? I personally don't mix triggers and lions together due to difference in temperment, but many have success with it. I just don't think a lion is happy with a trigger in the same water. Not that I haven't tried it (cuz I have), just won't do it again. HTH and just my 2cents.