Be careful to understand the difference between a flush valve (on the concentrate tube), and a DI bypass (on the permeate tube). They are two very different things that serve two different purposes.
Russ
Thanks for your comment. I do understand the difference however from my testing it seems like the bypass actually works way better then the flush kit due to the simple fact that you're monitoring the amount of TDS leaked before switching on the DI stage. The big cavet here though is that a flow restrictor on the drain side of the membrane is kind of a must as the bypass alone would waste way too much water without the restrictor and it also depends on the area.
In my area the tap water line has 1000+ TDS which means I have to run both flush kit and bypass for about 3 mins to reduce TDS down to mid 60s whilst some areas that have a tap line that have a 100 TDS would probably be way better off with just the flush kit.
At this point though I think we might be trying to over optimize so I follow a general rule of thumb:
1) Try a flush kit first preferably an auto one so just in-case you forget to flush your membrane it doesn't just kill your DI
2) If option 1 is not enough go for a bypass
3) If both methods still produce very high TDS then you might want to change the RO membrane
4) If that still doesn't fix it go for a booster pump and slower flow rate membrane
5) If by then you still have high TDS (like I do) then the last resort is to go for a fairly complex system of dual filtration.
The filtration I'm talking about in #5 is where you take the product water from membrane #1 and pass it through a secondary membrane with a booster pump and pressure tank.
With this said I highly doubt anyone in the US will have the issues we face here I've seen a couple of US water reports and you guys never really exceed 500 TDS so dual membrane would be too wasteful.
