Just picked up some NAACO Zip Fix--the concentrate is relatively cheap, and the ingredients are only Ammonium chloride and Potassium Metabisulfite. No acetic acid. Any reason why a bit of metaborate or carbonate added to it could make a good alkaline fixer?

Larry

PS. I've done this successfully with Ilford's Rapid Fix, except that since it contains acid, quite a bit of carbonate is needed to bring it to the alkaline side of the divide. 2 TBS. per liter of film strength. And it also produces a fairly strong ammonia odor.