PE: Thanks! I should add that all C-41 work is done on test shots. I have a reel of important material sitting here. I would not process that in any C-41, homebrew, brandname, whatever, until I know I can produce stable, calculateable results in my setup and way of working. With B&W I would be a bit more risky simply because its is not as sensitive and I am much more aquainted with it.
Nick: Just mixed up a new batch of chemistry (Fotospeed) with destilled water, demineralized actually, and seem to have lost one 'effect'. The shadows in some, not all, -2 exposed shots had a slight magenta cast. Though I am not to sure on really attributing that to the cleaner water.
srs5694: Great that you jumped in. Thanks for your experiences. Good to know. I have to start writing up mine with Fotospeed. I am new to C-41 self processing myself. Pushing a roll through a minilab I don't think counts
After my first film was completely bad - all the mids and shadows were green (completely underprocessed) - I went for systematic testing. I have done about 8 runs just with water to see how the temperature drop (from ca. 40C to 38C after about 20..30sec). Next were runs the cheapest film I could find and done test exposures. Initially they went from -3..+3, now I am back to -1..+1. I would do a series of test charts and 'real' situations where I would take notes on spotmeter readings of the scene. Suggestion for testing: take the same shot sequences 3x over, cut the film into thirds and process each part under different conditions. Promised, more details in a new thread on Fotospeed