Well, 420ppm is high, prolly a bunch of rust in there. I'd expect it to be down in the 400-410 range after the pre-filters. Is the sediment filter rust brown now or is it still noticeably white? Your pre-filters may be used, but they may still be OK. A properly functioning RO membrane would bring 420ppm in down to around 4ppm out, so it either needs flushing or replacing.
Btw, 80 gallons of RO means the pre-filter membranes saw 320-400 gallons of water cause your discharge is one gallon of RO per every 3-4 gallons of waste. Still nowhere near the 3000g service life. I'd imagine they're prolly still OK. You KNOW they're spent when the TDS rises after the pre-filters, that's a sure sign of a spent pre-filter.
Btw, 80 gallons of RO means the pre-filter membranes saw 320-400 gallons of water cause your discharge is one gallon of RO per every 3-4 gallons of waste. Still nowhere near the 3000g service life. I'd imagine they're prolly still OK. You KNOW they're spent when the TDS rises after the pre-filters, that's a sure sign of a spent pre-filter.
