Correct/best rust converter

[Mike Two Moons]

Hello:
I am currently in the process of replacing the wooden rub rail bolted to the side of my steel hull. After 15 years, I tired of spot fixing rust which appeared behind the rub rail, so it all was removed and I am rebuilding the contact surface.

In the past I have used a product which contained hydrochloric acid to convert the rust. It turned the rust black, but necessitated flushing with water before applying any sealing coat. I am told to stop the acid from continuing to work.

During my recent trip to the local chandler, I purchased the recommended converter that turned out to be phosphoric based.It turns the rust mid brown and leaves a chalky residue on the surface which can be scratched off with a finger nail. I was also told not to flush the surface as with hydrochloric acid.

Due to colour differences, I’m not sure the phosphoric has done what is expected. Plus I’m inclined to take a green scrubby to the phosphoric surface before starting the epoxy layers, to provide a solid surface.

Can any one suggest what is the correct/best rust converter to use?
Will applying hydrochloric acid onto the phosphoric converted rust provide any benefit at this stage? I appreciate any views.

Thanks