Below are some photos of a water tank used for potable drinking water which was rehabilitated using the descaling, cleaning and application of epoxy process detailed below.

Chemical Descaling and Epoxy Application Process
      Use ScaleAway circulating pump to supply ScaleAwayBIO to Water Tank.
      Add ScaleAwayBIO to water tank for 6-12 hours to remove scale build-up and rust from inside of water tank.
      Neutralize descaling chemical inside water tank with ScaleAway pH-Buffer non-toxic neutralizer until pH 7 is reached.
      Flush neutralized chemical from water tank to sewer.
      Scrub and power-wash residue with high-pressure washer from inside of water tank.
      Add make-up water to the water tank to rinse out residue, drain tank to sewer.
      Abrasive blast inside of water tank with Silica Blast Beads.
      Vacuum out silica beads.
      Wipe all inside surfaces with ScaleAwayEpoxy151 solvent.
      Paint non-toxic epoxy for potable water systems to inside of tank to a thickness of 200-300 microns.
      Allow coat to dry for 12 hours.
      Fill water tank with clean water.

Please note the following:
      The protective galvanized coat applied when the tank was new has corroded off over time, thus the formation of rust with the water scale build-up.
      Due to the corrosion of the protective galvanizing, the water tanks will form new rust deposits.
      A coat of non-toxic epoxy will need to be applied prior to the water tanks being put back into service.

In an effort to minimize future scale build-up in your water tanks, it would be prudent to install an Ion-Exchange Water Softening System.

Information on Ion Exchange Water Softening