Hi J & M The larger the amount of material you are trying to mix, the more important the pump performance is. Most of the Hydroseeding manufactures of jet style machines us a Monarch or a Banjo Pump. If your unit is in the 300 gallon range a 3 x 3 pump would be the minimum I would suggest. If the machine has a good design you could use about any 3 x 3 pump. You could add Homelite and Honda to the above list of pumps. If you are larger than 300 gallons with your tank I would suggest you try to find a 4 x 4 pump. You can mix 500 gallons with a 3 x 3 but you need a good design. Monarch introduced a new line of pumps a year ago that were specifically designed for use in a hydroseeding unit. To me it is the best pump out there for a hydroseeding application. I will say that since it was your actual question. Banjo is a pretty good pump also and may be easier to find. You would have to get the Monarch from someone like us who build units where the Banjo pump is sold by a lot of people.