how do you clean your steel roof?

[terracore]

So we contacted a roof cleaner and they offer a regular pressure washing and a soft wash. The soft wash includes a pre-application of a chemical that allows the roof to be cleaned without high pressure to protect the paint and then ascorbic acid afterwards to neutralize it. They weren't trying to steer us towards one or the other saying it was personal preference other than saying the hard wash would be required before repainting but that doesn't apply to our situation. The roof is 15 years old and other than being dirty looks almost brand new so I'm thinking its probably better to try not to punish the paint, but I don't know if the soft wash is required and it costs twice as much. They did say the soft wash would make the roof more slippery when they were done. I don't know if that's a good thing or a bad thing for the roof but I don't plan to throw a party up there.

These are the quotes:

Roof cleaning - Roof cleaning 1.0 $670.00

Roof cleanings will be done with specialized Pressure washing pumps that output lower pressure, but a
higher volume of water. This ensures your roofs screws and gaskets will be in the same shape after the
cleaning. Normal pressure washers have a tendency of prematurely wearing down your roof and seals. Post
cleaning we go the extra step and rinse down the eves and fascia of any debris that came out post cleaning.
We will provide before and after photos of your roof so you can also check out the condition of the roof post
cleaning.
Cleanings also come with an 9 point inspection + Mild remediation
-Fixing loose or missing screws or nails
-Screw gasket inspection and repair (up to 15)
-Vent Pipe Sealant inspection & repair
-Ridgecap inspection
-Valley Inspection
-Inspect roof paint
-Inspect rust
-Structural Movement
-Verify proper installation (roof)


Soft Cleaning of the Roof $1,248.00:

The difference between Soft Washing and traditional pressure washing is the very low pressure used during
the cleaning, and the need for an algicide to kill the algae growing on the roof.
The algaecide we use is Sodium Hypochlorite the active ingredent is similar to bleach.
Application process ensures minimal oxidation is disturbed and paint does not get removed. Since little no
no oxidation is disturbted there might be footsteps left where our footware rubbed. Heavily soiled areas may
need the use of a soft tipped brush to agitate the mix.
Once the roof gets clean Ascorbic Acid will be applied to neutralize any traces of the SH.
Cleanings also come with an 9 point inspection + Mild remediation
-Fixing loose or missing screws or nails
-Screw gasket inspection and repair (up to 15)
-Vent Pipe Sealant inspection & repair
-Ridgecap inspection
-Valley Inspection
-Inspect roof paint
-Inspect rust
-Structural Movement
-Verify proper installation (roof)

So other than the expense ($670 versus $1,248) what are the opinions versus the two options?

TIA.