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Self-weighted disc, rod and tube diffusers — drop them in and they stay put
No base, no bricks: these diffusers carry their own weight. Weighted discs (3"–7") give a tight fine-bubble plume for ponds and tanks; flexible rod diffusers (9"–36") and the 8" circle lay a bubble line along the bottom; the 12" weighted tube is a dense curtain for holding tanks. All are rated for depths under 8 ft on Hakko pumps.
- Discs
- 3", 5", 7" weighted
- Rods
- 9, 12, 15, 24, 36" + 8" circle
- Tube
- 12" × 2" weighted
- Fittings
- 3/8", 1/2", 5/8"
- Depth
- < 8 ft
Image coming soon
Mystic Koi’s take
For a koi pond, a 7" weighted disc per 3,000 gal on a Hakko 40 is a good baseline. Rods are what we use in quarantine and show tanks — one 24" rod gives a wall of bubbles with almost no noise.
Sizes
| Model | Type | Size | Ship weight |
|---|---|---|---|
| MD-3W | Weighted disc | 3" | — |
| MD-5W | Weighted disc | 5" | — |
| MD-7W | Weighted disc | 7" | — |
| OD-8 | Circle rod | 8" | 0.44 lb |
| RD-9 | Rod | 9" | 0.26 lb |
| RD-12 | Rod | 12" | 0.33 lb |
| RD-15 | Rod | 15" | 0.42 lb |
| RD-24 | Rod | 24" | 0.64 lb |
| RD-36 | Rod | 36" | 0.95 lb |
| MTD-300W | Weighted tube | 12" × 2" | — |
Rod/circle diffusers: 1/2" ID, 0.77" OD. Pump-to-diffuser quantity chart available from Matala.
Pairs well with
The science: why bottom aeration matters more than a waterfall
Oxygen enters water at the surface, and a diffuser’s rising bubble plume lifts bottom water up to the surface in a continuous loop. That circulation is the real work: it de-stratifies the pond, keeps the bottom from going anoxic, and carries ammonia to the filter. Fine bubbles transfer more oxygen per cubic foot of air because of their larger total surface area and slower rise. Warm water holds less oxygen (about 7.6 mg/L at 86 °F vs 11.3 mg/L at 50 °F), which is why summer nights are when koi gasp.
- Matala Water Technology Co. (2026). Aeration product data — Hakko linear pumps, MDB platforms, membrane diffusers, Ez-Air Pro kits. matala.com.tw.
- Boyd, C.E. (1998). Pond water aeration systems. Aquacultural Engineering 18(1): 9–40.
- USGS (2024). Dissolved oxygen solubility tables (fresh water, sea-level).
Questions we get about the diffusers
How many rods can an HK-40L run?
Roughly two 24" rods or four 12" rods at full output; Matala publishes a pump-to-diffuser matrix we can send you.
Do they clog?
Rinse in pond water and scrub with a soft brush once a season. Soak in vinegar if calcium builds up.
Matala at Mystic Koi
Matala filter media and pond equipment have been a koi-keeping staple for decades, and Mystic Koi has sold and run Matala gear in our own systems since we opened in Upland, California in 1996. Everything on this page ships from Matala USA (Sea Life Designs) or our ¾-acre facility. Not sure what fits your pond? Call or visit and we’ll size it with you.