ro trouble double membrane help

[jackp1]

my ro system is 6 stage recently every filter has been changed & i still have 0.5 phosphate level & 0.02 nitrate level in fresh mix. so after scratching my head as iv asked for help on my ro system before & ended up arguing, people commenting without reading the original post correctly then making stupid suggestions. so iv come across a triple ro membrane system check out the link below, scroll down then click on the picture to zoom in & you shall see what i'm talking about.i want to do a double membrane set up so i have a spare membrane housing lying around & i was thinking of fitting it to my 6 stage system. the query is about the way you join the membranes, after going through the first membrane the fresh 1st membrane outlet will go into a t piece & the brine line will go into the entrance end of the second membrane housing, theoretical the second fresh membrane housing outlet will also go into a elbow piece then into 1 side of the t piece & then direct the flow from the t piece of both membranes into the di chamber & that water should be tds 0. so what ya think any good that's if you can get your head around what i'm on about. i also wouldn't think i would need a flow restrictor on the second ro membrane housings brine line.
http://www.windowcleaningwarehouse.co.uk/shop/ro-systems/450-gpd-ro.html

[fishdip]

I dont no what will work for you but im having the same problem with my ro so I hope some one has a good idea

[Squint]

That's how my double membrane system is setup. I added a booster pump as well. To deal with the increased flow rate due to the dual membranes and booster pump, I had to add more carbon and DI cartridges.

[chadfarmer]

maybe its the salt

[fishdip]

I know in my case its not the salt as I test just the ro water and still get .10

[Squint]

Maybe you need a new DI cartridge or more of them?

I have 3 DI cartridges and 5 carbon and may add even more one day.

[jackp1]

same prob here my ppm is about 10 after adding 3 pods & cleaning out every filter london water is terrible 350ppm