# new 3 stage ro unit, tds a little high?



## h1234 (18 Sep 2020)

i have a new 3 stage ro unit,
now in the past i usually get about 16ppm readings with my old filters
now it seems I'm getting 28-30ppm my tap water tds is 310ppm
any reason for this could the membrane provided be the problem?


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## lilirose (18 Sep 2020)

With a new unit you need to flush about 20-30 liters through to remove the carbon dust and other various contaminants from the manufacturing process. You know it's done flushing when you get a reading similar to the old one.


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## h1234 (18 Sep 2020)

i flushed the unit for over 2 hours yesterday night and now again for about a hour, they are going down by a few number but nothing much
also when i first switch on the unit i get tds readings of about 80ppm after a few minutes the drop back to the 30 range


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## lilirose (18 Sep 2020)

If it's a 50gpd unit, you need to flush it for about 4-6 hours, in my experience. If it's going down then I suspect it needs to be flushed a bit more.


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## h1234 (18 Sep 2020)

yh it is. il leave it on for a few more hours and see


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## Andrew Butler (18 Sep 2020)

Hi @h1234 
Am I correct to think this is a new unit and not replacement canisters?
You should be able to get 0.0 TDS really, as @lilirose says they sometimes take a bit of flushing but that's quite a lot.
Get a pump on it, I found it so much better using one that had auto flush etc and worth it's extra expense easily.
I hope they start pushing through 0.0 soon, you could always add a DI cartridge on if it's not already on there but is even more resistance, I know.


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## h1234 (18 Sep 2020)

yh it a whole new system, left it on for like 4 hours now, tds is at 26ppm, its usually half that number
.you guy think maybe the membranes shot?
its one of those cheap 3 stage units from eBay.  
this time the ratio of waste water to Ro water is 50/50
usually its like 70/30 waste to ro with my old filter.
any reason for this change in this quite significant waste to RO production.


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## h1234 (18 Sep 2020)

including yesterday its been flushed for like 6 hours now or more tds has gone from  35ppm  to 26ppm


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## Andrew Butler (19 Sep 2020)

I no longer use RO/DI but  brought a Vertex unit when they first brought them out a few years back and that pumped, flushed etc automatically and I never really had much of a run in time on filters. Quality units and canisters are worth the investment in my opinion, quicker production, less waste, auto flush etc. No idea what's on the market now and I was fortunate that the retailer put the wrong price up so was £100 cheaper than it should have been.

Have you ever wondered if it's your TDS meter? You should be able to get a 0 reading and even the 16PPM from your old unit is well above what you should expect.

Just my opinion, maybe a question you will get better response and experience from a reef forum.


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## Nick potts (19 Sep 2020)

Depending on the brand, RO membrane quality, pressure etc the TDS of the water is going to differ a fair bit.

As a general rule, an RO unit working at maximum performance will have an efficiency of about 98%, most important is the water pressure of about 60-80 psi but different units have different requirements. Then there is prefilters, water temperature etc which all affect performance.

I would keep it flushing for a few hours and if needed add a DI unit.

As a comparison, my tap water ranges from 40 to 70 odd TDS and even my RO unit would not bring this down to 0 without a DI unit. I usually get 1-2 TDS after the membrane.


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## h1234 (19 Sep 2020)

yes but i have another filter the same one and the product water was coming out at 16ppm. so somethings is not right


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