I notice when first turn on the valve to collect water, the output at the membrane read out only 008, as time goes by.... this reading went up, say 125 which is about 16 hours continously running () . Is this normal? Thanks.
You could always swap the TDS meters to see if they read the same on the other side. To flush the membrane there usually is a valve on the flow restricter or a valve that bypasses the restricter. You can let that run a few minutes to clear any gunk from the lines and see if that helps. There is a good example of it on the bulkreefsupply site.