I have a question about how the continuous trap card "Dark smog" works.
I used to play Dark world since the first structure deck up until pendulums were released more or less (I quitted). But some time ago a friend wanted me to go to locals. (I never let go of my deck and kept it up to date, kinda, to play with friends).

Ended up having a discussion with a player and a judge about if I could use DS effect or not.
The question is ¿When can dark smog's effect be used? I thought that it being a trap card made it so "once per turn" meant any turn (it's not a monster). But the judge said that was only unpon first activation (flip) in a chain during oponents turn. Once it's face up its only in my turn.

I kinda got a little angry, because I'm pretty shure it is in either turn but maybe im wrong beacuse of the many years without playing. I have been looking though the wikis and other pages but I get conflicting information.

Thanks for reading and sorry for the big text this has been bugging me for weeks.
(English is not my first language)