Catechol or pyrocatechin developers (example: Pyrocat-HD) oxidize much like pyrogallol developers (example: PMK). When processed in trays or tanks with intermittent agitation, the oxidation occurs at a relatively controlled rate, which contributes both to the stain and the lovely tonality. With continuous agitation (rotary), both type developers oxidize too rapidly and underdevelopment will result.(posted 8288 days ago)I know of two ways to deal with this. One, and by far the simplest, is to increase the amount of developing agent (typically part "A"). I would try somewhere between 50-100% increase. With the activating agents used in most catechol or pyrogallol--sodium metaborate in PMK and sodium or potassium carbonate in catechol types--it will probably not be necessary to increase the activator.
The other alternative is to an additive to reduce the oxidation. I'm having a brain lapse at the moment and can't think of the chemical's name, but the trade name is Calgon. Also, I'd have to check my notes- -which are not with me at the moment--to tell you the amount to add, but if someone else cannot provide this, email me and I'll give you a starting point. I believe Gordon Hutchings mentions it in his Pyro book.
As I recall, the rollo pyro formula uses *both* these fixes.
Ahhh, it's call EDTA (Calgon)!