So I live in Jakarta when usually the temp can get to 31°C and all my fish are used to it (Yes! Including my rosy barbs and angelfish!)
But sometimes the water is around 26°C before the ich came.
I bought a heater and aquarium salt to treat the ich and when I heat the water to 30°C, my fish swims normally and never goes up. Usually when I come to my room to study, they will go up and beg for food in normal water temperature (24-26°C) This time, no they just swim and only goes up to take an extra breath. Only my angel and goldies does that (Yes, I just realised that I'm not supposed to mix goldies with tropical fishes

)
Any idea what is happening with my fish when the water is cold? Perhaps an unseen or inner ich?