I use Aluminate by Warsaw. My local dist carries it. I clean one bay a week. I have FRP panels. I mix it 5:1 with water and spray it on with a hand pump sprayer. Wait about 5 minutes and rinse it off with the HP gun. Afterwards, I spray the walls with RainX and rinse. The FRP panels had "stains" on them when I bought the wash, and I have had no luck removing them, but I am positive we have no new stains. I think the RainX helps keep that shiny new look and helps keep the panels clean.
I also use this product for years, its a great product, it is made to clean frp panels, it also cleans stainless, aluminum, block, brick, painted block or brick, I use it straight from the 5 gal container, it is 20% hydrofluoric, I have used it wearing only shorts, sneakers and a tank top, you have to be careful not to splash it on you, they put muratic acid in it so you can feel it burn when it gets on you, they say you wouldn't feel the hydrofluoric until it starts burning through your skin, I heard it is calcium seeking so it goes straight for your bones, but I believe at the ratio that Warsaw sells it at won't hurt you if you are careful, I always wears eye protection. They say that Nitrile is the only safe protection to use as it will permeate rubber, vinyl or latex. I bought a full body green acid suit years ago to use when applying this product but never used it.
From Wikipedia:
Safety
Hydrofluoric acid is corrosive and a contact poison. It should be handled with extreme care, beyond that accorded to other mineral acids, in part because of its low dissociation constant, which allows HF to penetrate tissue more quickly. Symptoms of exposure to hydrofluoric acid may not be immediately evident. HF interferes with nerve function and burns may not initially be painful. Accidental exposures can go unnoticed, delaying treatment and increasing the extent and seriousness of the injury.[4] HF is known to etch bone, and since it penetrates the skin it can weaken bones without destroying the skin.[5]
HF chemical burns can be treated with a water wash and 2.5% calcium gluconate gel or special rinsing solutions.