Please Help on White Mark

[MareMare]

Thanks. I couldn't have don't it without all the knowledgeable people here because the people that work in the pet stores, sadly are not trained. When I first got the smaller tank and my fish, I was told I didn't need a filter or heater. I'm in NC, so yes maybe no heater now but it does get cold here. The water was cloudy after about a week so I decided to get a bigger tank so I could fit a filter and heater. That's when I joined this group. Thank you again!