Harvest & curing
by ONA
We'll only email you about this product — no marketing.
The ONA Block Odour Neutraliser is a solid, slow-release odour eliminator that uses terpenes — aromatic compounds found throughout the plant kingdom — to permanently neutralise unwanted smells rather than masking them with perfume. Developed by an ex-firefighter who needed something that actually worked in toxic environments, the ONA Block sits quietly in a closet, tent, or small room and diffuses aromatic molecules that bind to odour particles at the molecular level. One 170g block lasts up to 30 days, requires zero electricity, and is non-toxic to humans, animals, and plants.
All five ONA Block variants use the same terpene-based neutralising technology — the difference is purely what you'll smell while the block does its work. Here's a quick guide:
| Variant | Scent Profile | Best For |
|---|---|---|
| Polar Crystal | Clean, slightly minty, neutral | Grow tents and enclosed spaces where you want minimal fragrance |
| PRO | Industrial-strength, subtle | Spaces with the most stubborn odours — the strongest formula |
| Tropics | Warm, fruity, slightly exotic | Living areas where you want something pleasant in the background |
| Apple Crumble | Sweet, bakery-like, warm | Rooms where you'd rather smell dessert than chemicals |
| Fresh Linen | Laundry-day clean | Wardrobes, closets, and bedrooms |
If you're unsure, start with PRO. It's the workhorse of the range and the one we'd grab first for a grow tent. Polar Crystal is the runner-up — clean-smelling without being overpowering.
Standard air fresheners spray a cloud of synthetic fragrance that sits on top of a bad smell like cheap cologne on a sweaty shirt. You can still smell the problem underneath — you've just added another layer. The ONA Block takes a completely different approach. Its terpene-based formula doesn't cover odours; it eliminates them through three distinct chemical mechanisms.
Some of the terpenes in the ONA Block work through absorption — they pull odour molecules in and temporarily bind to them, trapping them. Others operate via adsorption, where odour particles are held on the surface of a solid rather than drawn inside. The third mechanism is straight-up chemical reaction: certain terpenes bond permanently to stink molecules and neutralise them entirely. The result? The smell doesn't come back when the air freshener wears off, because the odour molecules are gone.
We've sold ONA products for years, and the most common feedback is surprise at how well they actually work. Customers expecting another scented block come back genuinely impressed. The honest limitation? The ONA Block is designed for small, enclosed spaces — a closet, a tent, a car boot, a gym bag. If you're trying to deodorise an entire room larger than about 10m², you'll want to look at ONA Gel or the ONA Breeze fan unit instead. The block evaporates slower than the gel, which is exactly why it works so well in tight spaces — it's a marathon runner, not a sprinter.
Terpenes are volatile hydrocarbons produced by plants — the same compounds that give pine trees, citrus peel, and lavender their distinctive scents. The ONA formula uses a specific blend of these terpenes engineered to target and neutralise airborne odour molecules. As the solid block slowly evaporates at room temperature, it releases these aromatic molecules into the surrounding air.
Beyond neutralising smells, terpenes increase the oxygen content of the immediate area and have documented antibacterial and antifungal properties. When diffused into the air, they're capable of reducing airborne bacteria — which is partly why the formula was originally developed for use in fire-damaged buildings where mould and bacterial contamination were serious concerns.
The founder of ONA is an ex-firefighter with direct experience in hazardous environments. He needed something that could handle the acrid, persistent smells left after a fire — smoke damage, chemical residue, biological decomposition. Commercial air fresheners were useless. He developed the terpene formula specifically because it needed to be effective, non-toxic, and safe to use around people, pets, and plants simultaneously. That origin story matters: this wasn't designed by a marketing team trying to sell scented candles. It was engineered by someone who needed it to actually work in life-or-death situations.
| Specification | Detail |
|---|---|
| Weight | 170g (6 oz) |
| Active technology | Terpene-based odour neutralisation |
| Duration | Up to 30 days |
| Coverage area | Small enclosed spaces (closets, tents, lockers, cars) |
| Available scents | Polar Crystal, PRO, Tropics, Apple Crumble, Fresh Linen |
| Toxicity | Non-toxic — safe around humans, animals, and plants |
| Power required | None — passive evaporation |
| Mechanisms of action | Absorption, adsorption, and chemical reaction |
Complete your odour control setup: The ONA Block handles small spaces brilliantly, but if you're running a grow tent with active ventilation, pair it with a carbon filter for the exhaust and place the ONA Block near any passive intake or zip seam where smells might leak. For larger rooms or continuous heavy-duty odour control, the ONA Gel offers the same terpene technology in a format that covers more volume — and the ONA Breeze Dispenser Fan actively pushes the neutralising molecules into bigger spaces.
One thing to watch out for: don't place the ONA Block directly inside a grow tent during flowering if the tent is sealed. Terpenes from the block can theoretically interact with the terpene profile of your plants and subtly alter their aroma. Most growers place the block just outside the tent, near zip seams or passive intakes, where it catches escaping odours without affecting the crop. We've heard this from enough customers over the years that it's worth mentioning.
The ONA Block is a solid that evaporates slower than ONA Gel, making it better suited for small, enclosed spaces like closets and tents. ONA Gel covers larger areas and evaporates faster. Both use the same terpene-based neutralising technology — the difference is coverage area and longevity.
Yes. The formula is non-toxic and safe around humans, animals, and plants. The founder developed it specifically for environments where safety was non-negotiable — fire-damaged buildings with first responders present.
A single 170g block lasts up to 30 days with the lid fully removed. Partially covering the lid slows evaporation and can extend its life by a week or two, depending on temperature and airflow in the space.
Place it outside the tent near zip seams or passive intakes, not inside. The terpenes from the block can interact with your plants' own terpene profile if used in a sealed space directly alongside flowering plants.
It eliminates them. The terpenes work through three mechanisms — absorption, adsorption, and chemical reaction — that bind to and neutralise odour molecules rather than layering fragrance on top. Once the odour molecule is bound, it doesn't come back.
PRO is the strongest formula in the range, designed for the most stubborn smells. Polar Crystal is a close second with a more neutral scent profile. For everyday household odours, any variant will do the job.
No. It works through passive evaporation at room temperature. Just open the lid and place it. No plugs, no batteries, no maintenance beyond replacing it when it's used up.
Last updated: April 2026
