[stuartb]

My TDS reading is high, about 55. I thought it would be somewhere around the 20 mark. I've changed the pre-filters and the resin now it reads 000. The tank is filling fast I think, and when I turn the tap to flush the system some water is still going into the tank. Never used to do that! If I turn the tap to the same position that I use to fill the system, I think the 350 ltr tank will be full in about 45 mins instead of the couple of hours it used to take. Does this mean my RO filter is on its way out? Had the RO about 5 years and I use about 300 litres a day.

Any help appreciated,
Very confused,
Stu

[colin purewater]

Sounds like time for new membrane mate

[PoleKing]

Take a Tds before resin.
Above 50odd... Adjust waste. Still high-replace

[Spruce]

My TDS reading is high, about 55. I thought it would be somewhere around the 20 mark. I've changed the pre-filters and the resin now it reads 000. The tank is filling fast I think, and when I turn the tap to flush the system some water is still going into the tank. Never used to do that! If I turn the tap to the same position that I use to fill the system, I think the 350 ltr tank will be full in about 45 mins instead of the couple of hours it used to take. Does this mean my RO filter is on its way out? Had the RO about 5 years and I use about 300 litres a day.

Any help appreciated,
Very confused,
Stu

You have to make sure your 4040 is always setup properly. Firstly, you need to make sure you have a 50/50 waste to pure ratio. The easiest way to d0 this is to fill 2 x 25 liter containers together, one with pure and one with waste. They should both fill at around the same rate.

Once you have done that then check your TDS output after r/o against your tap r/o. (You should have a rejection rate or efficiency of around 98.5% under ideal conditions. If it has dropped to below 95% then the membrane is on its way out. (example. 100 tds input and 2 tds output is an efficiency of 98%). At what point you decide to replace the membrane is up to you, but will hinge on the cost of resin needed to polish off the water after r/o.

It is easy to damage a membrane by closing the waste off altogether, even for a short time by accident.

If your membrane is good, then making water too fast may indicate that the waste isn't setup properly. But an 5 year old r/o membrane is most likely the problem you have and needs to be replaced.

[MATT BATEMAN (OWC)]

June at gaps water reckons you need more waste than produced, so not 50/50. Just had to replace my membrane due to wrongly set up waste ratio.

[andyM]

June at gaps water reckons you need more waste than produced, so not 50/50. Just had to replace my membrane due to wrongly set up waste ratio.

I think Gaps recommend 70/30 ratio.
But probably depends on water hardness. Softer water maybe 50/50 is ok? 

[Spruce]

June at gaps water reckons you need more waste than produced, so not 50/50. Just had to replace my membrane due to wrongly set up waste ratio.

I think Gaps recommend 70/30 ratio.
But probably depends on water hardness. Softer water maybe 50/50 is ok? 

I know that GAPS likes to recommend a much higher waste to water ratio. They also have to advise around a greater variety of systems,  water pressures and hardness.

I think we can easily get carried away and recommend something that works for us but may not be suitable for others. Thanks Matt for drawing my attention to this. Yes, it would be better to run a higher waste in hard water areas.

For me, I have a tap water tds of around 100 - 125 and water pressure of 50psi at the moment although it is mainly around 40psi. I don't have a booster pump and used an HF5 membrane with a waste to pure at 50/50.
I have an inline tds meter which is pretty accurate when compared to my hand held unit. (I test my hand held unit perodically against a known tds tester). At the moment my pure output tds is 2.

I don't know how long this membrane will last - its been in there a year so far and working exactly as it did when first fitted.

My previous 450 GPD had a 3 : 1 waste to pure ratio and those membranes lasted 6 years, but that doesn't mean that this 4040 membrane will do the same. However, I can live with a lower life span as we now have an 'endless' supply of pure water which we didn't have with the 450GPD - horses for courses I think the expression is.