Downy mildew? There are resistant varieties. Fungicides might work.

Thanks for the reply. I found a couple of fixes using baking soda. I'll be back.

Grow tent, not enough air circulation is probably the main cause.

Poor air circulation can be problematic if the humidity is high. Sounds like it was low. But it's hard to maintain low humidity in an enclosed structure. Was that really the humidity inside the tent?

Thanks for your replies. The humidity stays around 30% in the tent which is the same outside the tent set up in the basement. I also have a fan rated at 400cfm attached to a carbon filter pulling the air out and bringing fresh air in through screened windows. I removed the spotted leaves and sprayed the remaining leaves (top and underside) liberally with a baking soda/Murphy's Soap recipe found on the Internet. We shall see.

Fungicides are best used as a preventative. They don't cure the disease/fungus once it is on the plant, they just slow its progression. Also, be careful with those homemade sprays. Some can do a lot more harm than good. Best to test them on a few leaves first before dousing the entire plant.

Rodney