Been about 11 months since starting reefing. Including a salt mixing station fed with a 5 stage ro/di system. Incoming tds is 265 and output is 0. When replacing a heater in my 35 gallon mixing tank I noticed a yellowish scale and brown staining on the sides and bottom. The scale scraped off like dried paint. So I cleaned the tank with a scrapper and pad. I use fritz salt from day 1 and the DT, corals and fish, are doing well. I have two small circulation pumps in tank and a heater. There must be contamination in fritz salt as the tank is sealed and use only ro/di water. What are your thought in this, normal? Fritz? Etc? Should I change salt?