Ona Blocks are a dead simple method to adding odor control into your garden. By working with highly odor absorbent material and clean, light scents, ONA provides a powerful alternative to common home odor control appliances. ONA can be used in applications beyond simply indoor …gardens, they’ll keep cars, bathrooms, mud rooms, and anywhere that can tend to smell contained and with a refreshing odor. HTG Supply carries ONA supplies in a variety of scents to keep your grow room smelling fresh.