How and if to treat

[Lukeptb]

i have recently purchased two reeve's turtle's and have them separated they look fine and healthy both 1 and a half years old, one is around 3 inches and the other is around 5 they have been in a very small tank with no UV or heat bulb only source of heat being a heat mat which was very poor, also filtration was practically non existent.
all that taken into account the only problem i can see is that they open and close there mouths almost like gasping but pretty fast is this a respiratory problem and should i do anything to help this problem get better.

bought them as i thought they would be much happier in a large 400+ litre tank with all that a growing terrapin needs.

thanks for the feedback much appreciated