The two resin cartridges can last up to 300 gallons of water. It can not be recharged, but we do sell the replacement resin in various sizes. I will put a link to our replacement resin below for you. With you TDS being as high as it is, based on the chart below, I would assume it to be around 65-70 gallons per cartridge. In the manual it explains how to replace the cartridges or how to refill them. I will link the manual below as well.
Replacement Resin: https://www.rvupgradestore.com/searchresults.html?Search=CR+Spotless+Replacemen