New Tiger Salamander/Old Larvae questions

I've had a larval tiger salamander I've been keeping by himself in a 10 gallon since mid/early November. I picked him up because I thought he was going to morph soon, seeing as how his gills seemed to be receding. He was pretty skinny when I bought him and he has fattened up a good bit. I've been feeding him bloodworms, reptomin, and I fed him a few mealworms last night that I bought for my new morphed tiger salamander I just bought yesterday. I had no intentions of buying a salamander when I left the house yesterday, but stumbled upon one for the low price of twenty dollars and couldn't resist. I didn't need to buy anything additional since I already had a vacant 29 gallon terrarium just taking up space. So for now the morphed tiger is in the 29 with some coco fiber substrate and a couple makeshift hides from a "modified" coffee container. My question is: If I buy something like a shallow paint pan(the kind that ramps upward for paint rollers), fill it with water, and put that in the 29 along with my larval salamander, would that be wise? Would I have a problem with my new salamander being aggressive, or drowning?

Also, is there anything I can do to naturally "encourage" metamorphosis in my larva? I lowered the water level in his tank when he seemed like he was staying towards the surface of the water on the driftwood. However, he hasn't made any use of the land portion as of yet, and I haven't seen hardly any change in his body since I bought him other than his fattening up. I've also included a few pictures. The picture of the larva is when I first got him a few months ago. I'll try to get a picture of his current state up soon. And any other tips/feedback would be much appreciated.
He appeared to have been beat up a little bit. If I remember correctly, he was originally kept with like 4 other water dogs, possibly a fire eel, or a clown knifefish. I also read later that gravel isn't the best, however, it is mostly too large for him to eat, and I hand feed him so there is virtually no chance for ingestion.

Well, like a day after I wrote this my larval tiger salamander decided he wanted to start rapidly morphing. It's neat to see his change because he's a little different every day, and changing quickly. My morphed salamander is doing great, and is quite a bit more active than I thought it would be. Every couple of hours it comes out and makes a lap around the tank then re-buries itself.