Do NOT decrease agitation. If the film is too contrasty, either decrease the development time or increase the dilution.(posted 9094 days ago)Let me take a poke at agitation. Agitation CANNOT be too vigorous or violent, of course as long as things aren't being physically damaged.
"Gentle" agitation is often otherwise known as insufficient agitation, usually recognized by blotchiness, unevenness, lower density in a line along the center of a strip of negs, streamers of higher or lower density from sprocket holes and other really bad things.
Ideal agitation would be the removal of the film from the solution and plunging it back in many times during the total agitation period; that's the way it's done in a rotary processor. Another way of achieving essentially the same thing is nitrogen burst, in which nitrogen is blasted into the tank, but that's limited to high-volume hardware.
When using an ordinary rollfilm tank, use a double-reel tank. Put film on one reel and put it in the bottom of the tank and put an empty spacer reel on top. Use just enough solution to cover the bottom reel; do _not_ fill the tank. Follow the usual inversion routine. You could use two reels in a four-reel tank, three reels in a four-reel tank etc, as long as you leave a big air space at the top.
The way this works is that when you invert the tank the effect is as if you lifted the film reel out of the solution, then when you right the tank you plunge it back in. The entire surface of the film receives fresh developer.
As for your Pan-F in Rodinal, the change I'd make would be going to Rodinal 1:75 for the same development time. Of course you must run a test roll to be sure it's what you want rather than testing on "real" film. By going to a higher dilution the film will have a bit less highlight density and the grain will be slightly finer.
Water frothing over rocks has lots of specular highlights; you might say that it's all specular highlights. So what looks like a black spot on your negs may actually print just fine, so make some prints before changing film development.
For more than you'll ever want to know about the effects of agitation, see _Controls in Black and White Photography_ by Dr. Richard Henry.