I was putting him to my balcony until when he started to get black. because at first i thought i freeze him to death. I flushed him down before and flushed him down today morning too.

How are you keeping it? What type of water? How COLD did it get outside when it was outside?

he has been getting this kind of temperature for last month. Maybe a little warmer. But i mostly get him back inside when i feel like i ts too cold. I was watering him whenever i see his water tray dry.

I was using pure water for like 8 months then i couldn't find that brand for like weeks at shelves so i searched for another brand of water. It was labeled as pure water nothing else inside. I started to use it then i notice the black yellow leaves.

then i checked the webs8te and it says it has some kind of "protection" in it

You have to use rainwater, distilled water or reverse osmosis water ONLY. No other kind. VFTs can take short freezes. Only keep the soil moist, this is dormancy season.

The soil looks overly wet, but that could just be a picture taken right after you watered it. So it's either the leaves are dying from too much water or the leaves are dying their natural life-cycle. It almost looks natural, as leaves will begin to die off, just like any leaf of a plant. However, because some of your healthier leaves have black areas also, not just starting from the trap first, then I think you might have other problems. The water can be moist but not necessarily need it to be so wet.