Ok so I took over in taking care of my brothers turtles because he is a terrible owner and when I was at school my mom sent me this photo.

My turtle has foam thingy in its mouth and then it went away for a few days and it just happened again recently. it eats fine, it doesn't have any heater though, my brother rarely ever washed its little pool thing and it's really worrying me. Like when I went up to touch it today after school it got really aggressive and started hissing at me when normally it would just challenge me to a starting contest and only get aggressive when I brushed its belly. I need help you guys!