Look at Northern Tool. They have a backpack sprayer that can be pumped to 90 psi with the optional plug instead of the check valve. They also have a 60" brass wand available.

There are others on wheels that might offer more psi/volume.

www.hoosierpondpros.com

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).