Are you using the six-sheet Expert Drum or the ten-sheet Expert Drum?
Look at this instruction page from Jobo:
http://www.jobo.com/jobo_service_analog/us_analog/instructions/instructions_misc_expert_drums.htm.
The ten-sheet one should hold 500 mL of developing solution if it is loaded with ten sheets. Additionally, the maximum volume is printed on the tank itself. While I do not have mine in front of me, I can remember that the minimum is 210 mL, and I believe that the maximum is 500 mL. The six sheet tank should hold a maximum of 300 mL. If you are using 1200 mL, not only are you impeding proper agitation, but you are destroying your processor (assuming you are using a processor, as opposed to hand agitation on a roller base).
Additionally, assuming the ten-sheet tank, you are using a high dilution of HC-110 to do 2.5x80 sq-in. Kodak specifies a minimum of 6 mL of concentrate for every 1x80 sq-in. This means that if you are doing a full batch of ten sheets, your working solution should contain at least 15 mL of HC-110 concentrate ("syrup"). However, your 1,200 mL at 1:89 (
not 1:90, as you stated), contains only 13 mL of concentrate.
Now, I personally believe that this is a safe amount, because Kodak provides a rather hefty safety margin in their recommended minimums. I feel - based on trial and error - that you can get perfect results with 1/2 of the manufacturer's recommended minimums, so 7.5 mL is perfectly safe for that amount of emulsion, IMO.
However, if you were to go down to the proper amount of chemistry (Let's again assume the 10-sheet tank, at 500 mL.), at your dilution, you would have only 5.5 mL of concentrate in the solution.
Thus, it seems to me that
going down to 500 mL of chemistry, and a more standard dilution – like 1:31 or 1:63 – would help you out. If you did this, you would have the random agitation that Jobo intended when they designed the tank, and you would have enough concentrate in the solution to ensure complete development of all your film. Additionally, you'd be able to follow the on-the-bottle directions and easily mix your working solutions from a stock solution. Use 1:31 to meet Kodak's recommended minimums, and 1:63 to use half of these minimums.
To make 500 mL of 1:63 working solution from stock solution, mix 31.25 mL of stock with water to make 500 mL. 30 mL of stock to 470 mL of water will be absolutely fine.
To make 500 mL of 1:31 working solution from stock solution, mix 62.5 mL of stock with water to make 500 mL. 60 mL of stock to 440 mL of water will be absolutely fine.
Or you can use 1:49 to land halfway in between, and make the stuff easily mixable straight from the concentrate. (Just use 10 mL of syrup in 490 mL of water.)
