It's still not clear to me how re-using C41 developer would increase the risk of bubbles. Commercial C41 developer IME has a surfactant incorporated into it that promotes even wetting, which makes sense in the light of the short development time. Films can also contain surfactants, either for the same reason as above, or to obtain a favorable behavior of the liquid emulsion during coating. This can/will end up in part in the developer. However, there's a couple of reasons why these surfactants aren't really a problem - or, at least, shouldn't be:
1: regardless of any foaming, as long as the developer liquid covers the reels, there's no way the foam will interfere with development since the liquid developer will displace the foam.
2: as said, it's in the developer to begin with, so the problem would exist just the same with fresh developer.
What I can imagine is scenarios in which the following conditions hold true:
1: There's a surfactant in the developer and/or the film or some other compound that promotes foaming.
2: There's sufficient agitation for this foaming to become significant.
3: The reels spend a considerable amount of time statically suspended partly above the level of the developer.
Such scenarios are thus caused not by reuse of the developer, but mistakes elsewhere in the process.
All considered, the cause is likely elsewhere, not in the fact that the developer is reused.
Reusing developer (without replenishment) can indeed have other negative side-effects.
Yes, that makes perfect sense, one generally attributes these issues to insufficient developer volume or wetting agent contamination, however my tank and reel were bought brand new and never touched a wetting agent, as for volume, a 2520 tank takes 270ml for sufficient coverage of the reels, i always ran 500ml, then increased to 650ml as as suggestion from a friend. the more the developer is reused and replenished the more foaming starts to appear and that has been my experience with c-41 for a while now. i've read that it could be a change in pH caused by re-usage (with replenishment) but i don't have a reliable method to test that.
all measuring beakers, tanks, reels and the machine's tank are fully clean and haven't had any contact with wetting agents.
i've seen lower rotation speeds being mentioned as a way to aid in this issue but my machine only runs at 75RPM, so it unfortunately isn't something i can test.
the constant agitation shouldn't be allowing the bubbles to stick to the film but they somehow are.
my process is: the machine auto pumps the developer through the lift while the tank is spinning. at 18 seconds left i open the machine's lid, take out the tank and pour the developer into a 1L becker, then i put stop bath immediately and proceed as usual.
my jobo lift motor isn't working so i can't let the lift do the disposal of the developer, since it's being replenished that wouldn't be of interest to me anyway as the drain plumbing could contaminate the developer. i've experienced with different speeds and ways of removing developer from the tank but it didn't really make a difference IME
when i initially had these issues i bought new measuring beckers to do c-41 mixing but the problem never went away. i've had bubbles even when i used to develop with a stainless tank, but working with higher volume had solved the issue for me, on a rotary process it doesn't seem to make a difference so far.
it doesn't seem to be a super common issue but it certainly exists in rotary process tubes and there's a few different facebook posts about it. but personally i'm still avoidant of the idea of adding Edwal LFN to my developer, as generally suggested as a fix.
