Most DI tanks are refillable, when the old resin is spent you put in new resin job done. The thread about recharging resin is a different thing altogether. We throw old resin away but there is a process that recharges spent resin. This is the process that involves using acid. I think most of us can forget about that for the time being. In the meantime when your TDS reading starts going up empty the resin out of the vessel and fill it with new. DAI