Just need to be careful raising the humidity too much inside the house...even if it is in your basement. Probably the best way yet is one of those inexpensive room cool mist humidifiers.

Thanks Jay- I have one in there already. I guess I can add a second one. Right now my humidifier is on a timer to coincide with the lighting hours. Is this correct or should I leave the humidifier on 24/7

I would let the plants determine that. If they have been doing fine as-is, then leave it alone.

I have started using some trays with pebbles and water to add hmidity. I could not get hold of gravel so I am using marble chips. I just want to make sure that this is not problematic. The water will not react with marbel to form a compound harmful to the plants right?