Blagdon 50mm Pond Air Stone – Part 2875

Blagdon 50mm Pond Air Stone

The Blagdon 50mm Air Stone is a replacement diffuser for a compatible pond aeration system. Blagdon identifies it as part 2875 and lists it for Pond Oxygenator kits and the Koi Air 25, 50 and 65 pumps. It is supplied as a single air stone, ready to connect to the appropriate airline from your existing system.

An air stone spreads air from the pump into a stream of bubbles. The rising bubbles move water and encourage gas exchange at the surface. This makes the diffuser a useful part of an aeration system, but it needs a working air pump and suitable tubing: the stone does not generate air by itself.

Product details

Brand	Blagdon
Manufacturer part	2875
Barcode	755349028757
Diameter	50mm
Pack quantity	One air stone
Listed pump compatibility	Pond Oxygenator kits; Koi Air 25, Koi Air 50 and Koi Air 65
Included equipment	Air stone only

Match the spare to your system

Check the pump model and existing connections before replacing the stone. Part 2875 is a useful reference when comparing a worn diffuser with the replacement. The 50mm measurement describes the stone, not the diameter of the airline connection. Do not choose tubing from that dimension or force an oversized hose onto the small connector.

For a complete new installation, compare our Blagdon Pond Oxygenator kits. If you already have tubing and diffusers but need a replacement pump, our Blagdon Pond Oxygenator air pumps provide the separate model options. Check each listing’s contents so that you do not accidentally order an incomplete system.

Why air delivery changes over time

A diffuser can gradually become restricted by deposits and material on its surface. That restriction adds to the resistance the pump must overcome. Water depth, airline length, tight bends and control valves also affect the air arriving at the stone. A weak bubble stream therefore does not automatically mean that the pump itself has failed.

Inspect the route from the pump to the water before ordering several replacement parts. Check for a trapped hose, a loose connection, a closed valve or a visibly damaged stone. If one branch of a multi-outlet system performs differently, compare its depth and pipe route with the others. Equal-looking outlets do not guarantee equal airflow when the connected runs have different resistance.

Fitting the replacement

Switch off the air pump before disconnecting the airline. Remove the old stone carefully, supporting its connector rather than pulling hard on the tube. Inspect the end of the airline for splits or hardening and replace damaged tubing with a suitable size. A sound connection should hold securely without crushing or breaking the diffuser inlet.

Attach the replacement to the airline and position it in the pond or filter as appropriate for your equipment. Blagdon’s Oxygenator guidance advises locating the pump above pond water level to reduce the risk of water siphoning back. Follow the pump’s own instructions for positioning, electrical protection and any additional non-return arrangement.

Positioning and checking the bubbles

Choose a position that allows the bubbles to rise freely and gives the airline a tidy route. Avoid burying the stone in sludge or trapping it where servicing would require pulling the hose around sharp edges. Keep it accessible enough to inspect and replace without disturbing the entire pond layout.

Restart the pump and check both the stone and its connections. Look for a consistent stream appropriate to the pump and installation, and listen for any unusual change at the pump. Greater depth increases the pressure needed to deliver air. Do not assume that adding a deeper or more restrictive diffuser will give better aeration from the same pump.

Airline choices

Where you want the airline to remain unobtrusive below the surface, compare our standard sinking airline and Evolution Aqua heavy-duty sinking airline. Select a connection size compatible with the pump and diffuser, using suitable adaptors where the system requires them. Larger airline elsewhere in an installation does not change the connector fitted to this stone.

Black braided airline can also be useful in an appropriate air system, but it does not sink by itself. Consider the actual route and how it will be supported before choosing a hose. Avoid unnecessary joints and tight bends, and leave enough access around the pump for routine servicing.

Maintenance and related service parts

Blagdon’s Oxygenator manual recommends replacing air stones at least annually, with earlier replacement where conditions require it. Check them routinely rather than waiting for a complete loss of bubbles. If a stone is cracked, its connector is damaged or it remains restricted, replacement is more useful than continuing to force air through it.

If the airline and diffuser are sound but the pump still performs poorly, check the pump’s service guidance. Our Blagdon air-pump service kits are selected by the exact pump model. A replacement diffuser and an internal service kit do different jobs; diagnose the cause before changing components unnecessarily.