So far all I have used as a stop bath is tap water. I have a Patterson tank with the special hose they sell as an accessory. I find that 5 minutes seems to do a nice job. I might be over doing it, I don't know,I'm still new to this. I've been at it 3 years, but in that time I've gone through 3 of the smaller Arista 12(?)oz bottles of developer. The films I have used so far are HP5+, Legacy Pro,and Arista Premium 100.