I need advice with film developing, and please don't make the answer "get an expert tank" - that doesn't even come near my budget at this point). I have a drum consisting of a 2830 bottom and 2870 top, a kosher combination for eight 5x7s as far as Jobo is concerned, in a CPA2 without a lift. I'm getting weird staining on the negatives:

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I first thought this was due to low chemical levels in the tank during development, particularly of fixer. Jobo calls for 200ml minimum chemistry volume during development, and I was using 12fl oz (354ml) of HC-110 dil B and 300ml of rapid fixer, so at no point less than 50% more than the minimum. I verified that the film was loaded correctly, emulsion side towards the center. I later tried re-fixing the negs, but the stains did not budge.

Previously I got the same artifacts in the Jobo, but got clean negs when I tray processed the same film stock (TMax 100) in the same soups.

I know that others have processed sheet film in 2800 series drums with no ill effects. Any help or suggestions would be appreciated.