turtle not doin good

My friends turtle isn't looking very good.it was on its back in the water before...its now in its own tank.it wasn't eating anything today ....any ideas how to help it?she's only had it for 2 weeks.he was with her other 2 turtles wich r slightly smaller they are both healthy she's had them for 6+yrs.

 

What kind of turtle are we talking about, slider, mud, box, etc.... Are all the turtles the same species?

 

before rees, i was obsessed with reptiles, i know a thing or two, what size is the tank? what is the temp? does she have a heating pad or rock? how often does she change the water? what decor does she have? what does she feed? are the other turtle of the same species?

 

Questions above and do they have drinking water in a bowl? It should be separate from what they swim in.

 

Thnx for the replys guys....unfortunately he didnt make it....they are iin a 29 gallon tank at night and a kiddie pool during the day I chage the water once a week or so....not sure of the temps tho I kno the temps r the same between tanks they have rocks frm petsmart and turtle docks...they eat frozens lance/silversides and turtle pellets. 2 wer sliders and 1 was a painted slider? 1 of the non paiinted 1s was the affected 1.nothing has changed other then the addition of the new turtle in well over 2 years.

 

maybe just old age, or a parasite or disease or something.

 

thats what i said ....guess well never know