John, I routinely fix film with a rapid fix (Ilford Hypam or Universal Fixer) diluted 1:9. You have to increase the fixing time (I use 3 times clearing time as a standard and discard the fix before the initial clearing time doubles), but you can use it "one-shot" this way, which is great with pyro developers and a water stop which allows the alkaline developer to be carried over into the fix more than with an acid stop. I've communicated with David Carper at Ilford about the feasibility of this and had my practice confirmed. Also, my residual silver tests on the film fixed this way are A-OK. One just needs to make sure that capacities are not exceeded and that enough stock solution is present to fix the amount of film at hand (with a generous "fudge factor" of course.(posted 8054 days ago)Bill, although your fixing times at 1:9 seem a bit short to me (although I'm not familiar with the Arista chemicals), it would seem to me that the problem lies with the film itself. I at first thought of contact between loops of film on the reels prevented total fixation, but unless you made the same loading mistake three times (which is unlikely, but not beyond the realm of possibility). If refixing does not clear up the spots, a film flaw seems one reasonable explanation. you have other rolls from the same batch, you could develop one unesposed roll to see if the same flaws were there. If not, expose one roll under the enlarger to a low density and develop it to see if the flaws are present. If both come out clean, start looking to your equipment and technique.
Hope this helps a bit. ;^D)