I appreciate very much your help!
Sammonkie ,I understand now the steps I have to follow.But I still have another question.Isn't it a small amount only a teaspoon of salt in half a gallon (almost 2 litres)?
SpotsMama and Sammonkie I'm pretty sure he is in hibernation(brumination ) because he doesn't have his eyes closed most of the time but
ALL the time!He doesn't eat at all,anything..But he is still changing positions with his eyes closed..(I also don't use a heater yet)
I also had before some years a RES that every winter used to be in hibernation from about November until March and had the same behaviour as Bubbles has now!Unfortunatelly I had to give her away for some reasons,but she is in good hands now.(I aslo didn't use a heater then).
The reason I'm telling you this is that I know how they behave when they are in hibernation.
Another fact is that all the RES(if not all,the 90% of them) that are sold in Greece are in hibernation because none of the seller at the pet shops use a heater,uva lamps etc..
So Bubbles is in hibernation(brumination)..
SpotsMama as you said he's spread whatever he has to his new habitat.Do I have to change the whole water now?And then add the sea salt?What amount of salt should I put to the tank?(except for the solution..)
And another question,will it affect the filtration system?I have the filter working only 3 days(and only 3 days I have the tank and Bubbles).
Thank you again!
PS:I couldn't find a vet that knows about RES.Today I'll try to find at the pet shops I know ZooMed's Turtle Sulfa Dip. And where I can find sea salt?(I have table water,but as you said is not proper).Do they sell it at super-markets?