Haven't had any problems with chemical stain build-up yet. I've been using one for a year now. Not with fixer until the past few weeks. This was done in a separate tray. I think its because I drain the slots completely from time to time and give each slot one or two flushes with clean water. Maybe do this more often than the 3 month duration recommended. Have large bottles at hand to store the chemistry while cleaning then replace it.