If he stays in the tank you will need to continue to do the daily partial waterchanges until the tank is cycled. The temperature is probably not helping matters.
If you place him in the fridge, then stop doing the waterchanges and let the tank cycle.
Before you decide to put him in the fridge, check the fridge temperature, it has to be above 4C (5C+ is fine = our fridge usually sits at 5-6C).
If unsure, place a thermometer in a glass/cup of water and place in fridge. Check it in 20minutes.
If it's ok, get two containers with lids - icecream containers work well.
Fill both with dechlorinated water.
Put lid on the spare one and put in the fridge.
Put Charlie in the other container, place lid on, wrap in a teatowel (to stop fluctuating temperatures), and place in fridge.
Every day you have to do complete daily waterchanges. This is what the spare container is for as they have to be same temperature.
When you're ready to do the waterchange, I usually do mine in evenings:
Take both containers out of the fridge, try and pour as much of Charlies water out wihtout losing Charlie!
Then tip Charlie into the clean container, put lid on, wrap with towel and place back in the fridge.
With the empty container, clean it out with a mix of bicarbonate/baking soda and water; then pour some more dechlorinated water in it, lid on and return to fridge.
I found this the easiest way to do a waterchange.
But if you don't have the room use one container and a softdrink bottle for the dechlorinated water to chill.
The fridge will slow his metabolism down. The colder water will also have more oxygen in it, so no need for holes in the container lid. If your fridge temperature is between 5-8/9C he may not eat, if you do offer him food do so just before a waterchange.