Matala Weighted Air Hose is a self sinking air hose designed to sink to the bottom of your pond without additional weight. It is available in 3 sizes; 3/8", 5/8" and 1.0". The black color easily disguises it on the pond bottom. You may purchase it in 10 foot increments or 100 foot rolls. The 1.0' is available in 50 ft rolls. Choose 3/8" or 5/8" for Hakko 25L. The outlet port on the HK25L is 5/8" so the 5/8" hose will connect directly. However, you can reduce down to 3/8" with an adapter reducer (not provided) to use the 3/8" hose for HK25L. Choose the 5/8" weighted air hose for Hakko 40L through 100L. The outlet port on these pumps is 5/8" so the air hose will connect directly. Choose the 1.0" weighted air hose for the Hakko120L. The outlet on the Hk 120L is 1.0". Do not use smaller hose than 1.0" for the HK 120L. It requires this size hose in order to run cool. If you use a heavy duty 4 way manifold with the HK120L, you can use four 3/8" hose to deliver air to 4 diffusers. See the article Heat Control for Hakko.