298 is just slightly above the national average of about 250. Not that bad really. mine is usually over 800, never ever drops below 500, and can get as high as 1200. Using your TDS figures it shows your membrane is only 85% removal efficiency or rejection rate. Not good if you tested directly from the RO membrane and not from a faucet or pressure tank. Don't waste any money on DI resin replacement if the membarne is in fact that bad. A simple rule of thumb says for every 2% you reduce the membrane efficiency you cut your DI life in half! Imagine how long DI would last if you were operating at 98% rejection rate which is where you could/should be. A new Spectrapure membrane is on sale for $35 for batch tested and only $45 for individually hand tested and guaranteed better than 98% rejection rate 90 GPD membranes. Lets find out first if your TDS numbers are correct, then tme the waste ratio and get the temperature and pressuer and lets look at the system as a whole instead of throwing pieces at it that may not last.