Just watch the humidity leves during flowering because you don't want mold!!!

Another rule of thumb which most people do is they blow air up toward the light across the plants from the base. They do this to keep the hot air from the HID lamp away from the plants, then the extractor draws the air out @ the top while cold air is push in at the bottom.

Check 2 see if the fans are not blowing hot air down cause this will damage your plants.