I have not tried Arches Aquarelle for a long time. I have never been very successful with this paper, but that was then (probably at least 6-7 years back). The issue of density is serious. For me at least, tonality should be first-rate, just like a platinum print, only in blue, or is it not worth it.
Try tween 20 instead of fotoflo, or leave it all out. I actually found Saunders Waterford HP a good paper, but *only after a citric pre-coat*. I sometimes neutralize paper before in a 1% hydrochl. acid bath (which has to be washed out afterwards!), this often makes the paper more receptive, but I still need the citric pre-coat (though less of it).
How do you apply the first acid bath? Try not to pour it over the picture, but pout the acid first into a tray considerably larger than the paper, tilt the tray to move the acid to one side, carefully place the paper in that part of the tray not covered by the acid - make it stick somewhat to the wet ground - then swiftly move the tray into an even position, if necessary, lifting it in one move there were the acid was when it was tilted, so that the acid floods in an even move over the paper. Rock only very gently, and wash the paper also very gently (face down, gentle water flow only at the back), possibly add a little bit vinegar into the water. If you still observe flakes of blue coming off, you need to do something about your paper base (see above).
Once the paper is dry, the blues will be stable (provided you don't sprinkle some alkali on them).