I'm in the middle of moving my darkroom to a larger space (empty nester that I am!). One of the goodies I've been hoarding for a few years without space/incentive to plumb up was a Power's Fotopanel water temp control. http://tinyurl.com/6ycxvz Just now, in searching out info, I found an APUG'er who had the seals leak on his used unit (mine is also used). I've decided to plumb it with shut-off valves immediately before the intakes on the mixer as a safety measure. What I'm wondering about is the potential for my used unit to have scale build-up that I should remove prior to getting it all hooked up. Are normal de-scaling methods such as one would use on an espresso or coffee machine likely safe? I keep sulfamic acid here that I use for that duty but I don't know what the actual mechanism is inside the Fotopanel. Is it a non-issue and shouldn't cause worry or do these sort of units build up mineral scale? Any learned advice from users of temp controllers in general?