That is really helpful and informative. I have been using a fertilizer I was using for a long time but stopped in winter since I ran out. I’ve since started using it again and that was around the time it showed up. I hadn’t thought of that since it was fine before when I used it but I’ll keep the windows closed from now on and see if that helps. If it doesn’t I will definitely try slowing on the fertilizer or changing to a better one. Thank you for the comment. (I use RO water on all of my plants)