floating goldfish

Question
My Goldfish can't stay low.  He is currently in a "cage" (large mesh cup) to keep him low in the water.  It has been 24 hours.  We stopped feeding him and I tried to press on his belly a little to see if constipation was a problem.  He did have two poops yesterday that he couldn't release easily and they were thick as I usually can barely see the string.  
My fish has recently recovered from a fungus (black and fuzz on him) in the last month due to living his 1 gallon starter tank.  

He had a good week or two after being cured from the fungus and moving to a 10 gallon tank.  

Then he started living in the cave on the bottom of his tank.  Only to come out to eat his NEW food.  After hiding in the cave for a week, he began floating on the top.

My questions are,
how many days of non eating and cage action should I do.  

Is the cage really important, or should I turn off the filter (water current) and let him float on top...possibly drying out his fins?  

Can it be the new food?

Should I try the boiled pea thing, while he's in the cage?

Water has been completely (90%) changed since this happened.  I'm having trouble keeping my NitrITES below 1 ppm on a regular bases and I go thru test strips like crazy.  I have a 10 gallon Freshwater tank and use the Tap water dechlorenator stuff.  

Our snails just had babies, and I think fishy may have eaten some of them, which I read is normal, but I thought I throw it into to the puzzle.

Any suggestions or comments will be helpful. Thanks for your time and knowledge!

Answer
I would not recommend not feeding the fish for over a couple days and even that is iffy. As for the cage, I don't know what to say but I wouldn't keep him in there for long because he can get sicker.
I doubt the cage is helping; it is more than likely causing more problems. I would leave the filter on.
It could be the new food, try him with the old food and see if there is any improvement.
You can if you like, I have never seen the point in the pea thing.
Real plants are good for lowering nitrites and you can also buy some nitrite remover from pet stores. I would also add a carbon filter and ammonia remover (if possible) to your filter, it seems to keep the tank cleaner longer. The water conditioner is a good idea and would keep doing it.
Eating snails is normal so I wouldn't worry about that.