As I'm developing film at home. I have problem to keep temperature constant for: developer, stop bath, fixer.l throughout the process at 20C degrees.
What's the best practice to do so ? How do people usually go about it ?
Also does final wash also require 20C degrees temperature?
I process film in a three-reel Paterson tank. Assuming the dev goes in at around 20°C then experience shows that it doesn't change enough to worry about for processing times of up to about ten minutes. However this depends on what the ambient temperature is, and smaller tanks will drift faster: where I live it's generally not hot enough for temperature rise to be a problem, but it can occasionally be cold enough in the winter (we have no central heating so the house can get fairly cold in rooms we don't heat). In this case I fill a sink with water at around 20°C and just keep the tank half-submerged in that. Nothing about B/W is that fussy about the temperature being axactly 20°C - a degree or two either way is OK, especially if the temperature drifts slowly during the process.
No, the final rinse does not have to be at the same temperature, although you want to avoid large steps in temperature. So what I do is try and arrange successive stages in the process so they're 'heading for' the final rinse temperature. At this time of year it's all fine, but in the winter when the water is pretty cold I try and have stop, a few degrees colder than dev, fix a few degrees colder than that, and then perhaps I do the first bit of rinsing with water with a little hot water added to get that stage intermediate between the fix & the temperature from the cold-water tap.
(Parts of the process which happen at significantly lower temperatures also take longer, so if you fix at, say, 13°C in the winter then give the fix plenty of time to do its thing.)