Basement grow- dirty furnace filter ruined it

I'm growing in a basement, and a few months ago my plants (which had always grown beautifully down there) just started to lose their zeal, look unhealthy. When I replaced the clogged, filthy furnace filter, things instantly went back to normal. Rapid lush, green growth.

My question is- why??? What gas/toxin was the clogged furnace filter allowing to build up around my plants?

why ask why, just keep making sure they stay green. seems a little deeper than an air filter, but who knows could be.

Hmm fcking hmmm what is a furnace filter? Sorry Aussie here we don't have furnaces lol

Might have something to do with better air exchange and less spores (could have had colonies in your old dirty filter?).

yea gotta have that fresh healthy air. If the filter was clogged dust and mold spores, and o2 from your plants, and any nasty fumes from the furnace were most likely building up. Fresh air is up there with light and water as far as importance in a healthy grow.

I forgot to mention- I'm running four 6-inch vortex fans that exhaust up to the first floor. Could all this suction create so much negative pressure that it's somehow pulling the air back out of my HVAC system? Also, there's a sump pump near the grow. Not sure if that makes a difference.

Probably just didn't have good air EXCHANGE. Sure you were moving air around, but probably were not exchanging enough to let CO2 levels stay at least at ambient. Who knows though. Glad they are happy again!