There is no correct value for Potassium Bromide addition in film developers, since your film is out of spec and nobody can know for sure how much is needed to get fog level back down. Fortunately you can find out the correct amount for your combination of film&developer with little effort:
- In complete darkness put a short, unexposed clip in your film tank. There is no need to put the clip on the spindle, but make sure you have that black tube in your tank in the correct position, or light will come into the tank through the lid.
- Take just as much developer as needed to completely immerse the test clip and do a test run with this setup. Stop, wash, fix, wash again, then inspect the test clip.
- If that first test clip is not significantly fogged, you can develop without any extra restrainer.
- If that first test clip is noticeably fogged, start with 2g/l Bromide and do the test again.
- If the second clip is still fogged, go up to 5g/l, if it is completely fog free, retry with 1 g/l. If there is only weak fog, you are fine with 2 g/l.
Since your film is fogged from old age and/or improper storage, there is no need to fine tune the amount of KBr, since there will be some variation between film rolls anyway. If you want perfect and reproducible results, use fresh film ...
PS: If Bromide had no effect on Phenidone based developers, then please someone explain me why they put it in E6 FD. And in Crawley's FX-37. And in ID-68 aka Microphen ...