Hiya ian mate
First things first; have you contacted Gaps Water and discussed your problem with them?
They ARE the specialists after all!
Not as yet mate,i will monday morning...as it's getting worse now..
I take it that you do mean the tap/valve that gives the back pressure to enable the membrane to work? - with such a low mains pressure the second gauge will hardly register at all, and will only do so as you begin to close the drain valve, thereby actually building up pressure for it to resister!
Yes i do mate,the drain valve.......so that's the norm then...i can tick that box
If you close the valve too far you will quickly clog up the membrane, especially with such a high tap water TDS reading.
I don't know what ratio of waste to pure should be with a low pressure 4040 R/O, but with a standard 4040 R/O, although you can achieve a 50:50 ratio of waste to pure, the lower the waste part of the ratio you try for will also reduce to potential lifespan of the membrane.
Right ian mate,i was playing about with waste ratio when i first got system & gap's told me not to bother,the membrain will be happiest when the tds is @ its lowest....so i got tds down to 14 then marked psi gauges & drain valve for future refrence...so i never finished the waste ratio,but theres a lot more going to drain.....
I know nothing about the use of a water softener setup used in conjunction with an R/O, but I'm presuming you are using it as recommended by gaps?
Ditto the regeneration of the beads?
on my instructions ian,it recomends me to use a water softner in hard water area's......so iv used a old di vessel bottle & bought softner beads & filled the bottle with the beads ,then attached it after tap & before filters etc........then i disconect it to flush salts through,until all salts have gone....then connect it again to system...
Mind you ian,im sure this was okay until i added this softner...im not sure......
I wonder if i disconect it then flush again without softner.........its flushing now,gunna leave it to flush for a hour with softner on see if that's any better as you asked i hardley never flush it.....only for 2 minutes couple times a week... :
With such low mains pressure, perhaps you could try opening your drain valve fully and flush your membrane for an awful lot longer than 15 minutes?
My own mains pressure is 65 psi, and prior to EVERY use of my own 4040 the membrane is flushed for 20 minutes before closing the drain valve and beginning the production of pure water.
You do flush before every use of your R/O don't you?
I'v NEVER FLUSHED IT LIKE THAT DUDE 
Like i say ian mate,im flushing it now for the next hour to c if that improves it....
I'll post later with a progress report
Thank you so much for you input my mate....ya sound fella Take care ian & kind regards
Justin
Hiya luther1 m8
As a 4040 reduces ppm by 98% so your ppm in of 550 should produce water out at 11 or so ppm. Changing pre filters generally doesn't change ppm reading just the longevity of the membrane. Can you manually adjust your valve to produce more waste and therefore reduce ppm reading?
Thank you dude......
I thought it should be better than that reading man
Steve,did ya get that man???
yeah luther1 i changed filters and never made diffrence....wot a waste of money
I'v also played about with drain valve & cannot get it any lower bud......
Big thank you for them figures man.....good to know what i should be getting
Thank you luther1 mate
Take care & kind regards
Justin
Carnt help thinking guy's...is it this water softner...it was okay till i put that in,then bout a week or 2 later it started creeping up 
I will phone gaps morro...& c wot its like after a good flush in a hour or 2.....i carnt belive this fella's
Take care guy's...ya sound
Justin
