Hi, I've just changed all 3 filters in the Merlin and let it run for about an hour with a decent booster pump and my tds reading is 45ppm. The tap water is 475ppm before RO does this sound about right? Seems a bit high to me, tbh i'm a bit disappointed.
I'm a little puzzled with my merlin too.
The TDS from RO had gradually climbed to about 30/31 (tap TDS c. 200) and recently, the production of pure was down to about 400 litres a day. Anyway the pre filters were due for a change so I ended up changing membranes too. The production has shot up as I expected (about 60 litres an hour) but the TDS has climbed to about 35 - even after running for a while. I do know that membranes take a while to settle down so hopefully this will improve over the coming days. I may have to ease the waste restrictor (for lower post RO TDS) and face a higher water bill. I have pressure of 45/50 with no pump. Now that I'm on a meter, I can see me going the low pressure 40/40 route eventually.
My suggestion would be to give it a couple of days for the membranes to settle down a bit and to ensure that you take your readings when the RO is at least 10 minutes after a start-up (TDS can take a few minutes to drop after starting).