I use an aquatic life 4 stage ro/di unit. With the filters that came with it, after flushing I was getting 0 TDS out of the RO before di. After 6 months of use ive been getting about 4 TDS. Today, after changing the filters it started at 15ppm out of the ro and was down to 10 ppm within 15 minutes of flushing. Ive been running the system for close to 2 hours and is still reading 10 TDS out of the RO. Could this be a bad membrane? Or just keep flushing?