FireBelly Newt help

I have had my newt, froogle for almost 3 months now. I have his tank setup where in one side the gravel is a little higher than the other side and put some rocks that forms a little tunel just like he likes it. In the other side it has a little gravel on the bottom and free space for him to swim around in. But he never leaves his cave. It is very rare when he does and also he never goes out of the water completely. He has space on top of the rocks to climb out if he wants to. Ive put him there sometimes but all he does is go back into the water. Is it normal for him to just stay under his rocks and to never come out? Is it also normal for him to stay in the water all the time and never come out completely? Is there something I should add to the tank that he would like?

Also in regards to food I heard it is better to change is diet at times to offer different food. I currently only feed him black worms(Live) he loves those and eats them up in seconds. Ive tried to feed him newt pellets but wont eat them, however if i put some pellets in between the worms, he will eat them accidentaly when he eats up the worms. Is this a good idea to do just to swich up his diet at times? I feed him every 2-3 days. He is an adult and is about 4 inches long.

I opted not to put a filter in his tank so i change half of his tank water once a week and put some drops of a conditioner for amphibians to take all the bad stuff out of the water. Anything i might be doing wrong that is not making him active? Anything I can or should change?

His behavior sounds pretty normal to me. They like to feel protected, and they don't move around all the time like a fish would.

If he likes to stay wet, or in the water, I would suggest making the water deeper. This would probably mean removing some of the gravel (you only need a thin layer) and making a land area some other way.

Live blackworms are a good staple diet. This article may give you some ideas for variety, but blackworms are just fine:
http://www.caudata.org/cc/articles/foods.shtml

For a small tank, changing half the water weekly is probably OK. The only problem you may have is that dirt will accumulate under the gravel and that's hard to clean out. The water conditioner will remove bad stuff (chlorine, metals) from the NEW water you add, but it won't do anything to remove bad stuff from the old water.