It's happening at two different hospitals in renal, sterile services and endoscopy. All supplied with this brand salt from the same supplier. It shows up more in this tank because it's taller and thinner than our others, but the same residue is visible in all, a kind of grey sticky scum. It's suspended within the brine and sticks to the side of the tanks and my concern is that it is going to block up the brine intake. It don't think it gets through to the RO inlet filters, we would have seen it, and we haven't seen any reduction in their life. We've sent pictures back to the supplier so we'll see what they have to say.