Underwater Pressure Washing Gunite Pool

I have a 17 year old Gunite pool in great shape. It appears to have a somewhat rough and colored finish to the plaster - perhaps some form of pebble type surface, but not pebbles per se.

There are some black algae dots and stains along with some other stains on the plaster. When I drained the pool 1 foot below the tile line to close it last year I took the opportunity to use my electric (1600 psi, 1.5 gal) pressure washer to clean the exposed surface and it worked great!

However, when I try to use the pressure washer underwater it is ineffective at all but right against the surface of the plaster where it has very narrow coverage.

Does anyone have experience in this type of application with a more powerful pressure washer? Is this type of cleaning even possible/practical?

Thanks!

db

A pressure washer under water will not be that effective because the water slows down the jet significantly due to the higher density (~800x). So either you have to get very close or have an extremely powerful water jet. I think you would be better off draining the the pool and then cleaning it.