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High TDS reading coming out of RO (25-30)


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Evening gents, 

Hope you can help with this as my business partner and our usual window cleaning contacts are at our wits end with this. We decided to get into the window cleaning business about 6 weeks ago and purchased a load of equipment from a friend — this included a purification system (pre filter, 2 RO's and 1 DI) along with some brushes, poles and tanks etc. 

Pretty much since we got the equipment we've been getting a TDS reading of around 30 or so coming out of the RO, obviously this takes it's toll on the resin filter and we've already had to replace the resin once as the TDS readings were getting too high. We've done the following and still we're getting readings of 25-30 coming out of the RO:

- Had Thames Water come up to give us a dedicated line to improve psi/flow

- Purchased a pump to increase PSI going into the pre-filter (we generally get about 120psi now)

- Replaced the membranes in the RO and replaced the pre-filter (we did this today as a last resort thinking it would solve the issue)

 

Yet still, we're getting readings of approx. 30 coming out of the RO and now it's started to creep up to 5-6 coming out of the DI so obviously the resin needs to be replaced again.

Does anyone know what the issue could be? As I said we're kind of at our wits end so any help would be much appreicated!

Cheers,

Ryan

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3 hours ago, Ryan316 said:

Evening gents, 

Hope you can help with this as my business partner and our usual window cleaning contacts are at our wits end with this. We decided to get into the window cleaning business about 6 weeks ago and purchased a load of equipment from a friend — this included a purification system (pre filter, 2 RO's and 1 DI) along with some brushes, poles and tanks etc. 

Pretty much since we got the equipment we've been getting a TDS reading of around 30 or so coming out of the RO, obviously this takes it's toll on the resin filter and we've already had to replace the resin once as the TDS readings were getting too high. We've done the following and still we're getting readings of 25-30 coming out of the RO:

- Had Thames Water come up to give us a dedicated line to improve psi/flow

- Purchased a pump to increase PSI going into the pre-filter (we generally get about 120psi now)

- Replaced the membranes in the RO and replaced the pre-filter (we did this today as a last resort thinking it would solve the issue)

 

Yet still, we're getting readings of approx. 30 coming out of the RO and now it's started to creep up to 5-6 coming out of the DI so obviously the resin needs to be replaced again.

Does anyone know what the issue could be? As I said we're kind of at our wits end so any help would be much appreicated!

Cheers,

Ryan

Evening Ryan. Have you flushed the new RO membranes after being installed for approximately 2 hours and monitoring the output TDS at regular intervals 

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Neil Mitchell

About what I get get another DI vessel connect it after the original one to get more life out your resin .

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9 hours ago, Ryan316 said:

Evening gents, 

Hope you can help with this as my business partner and our usual window cleaning contacts are at our wits end with this. We decided to get into the window cleaning business about 6 weeks ago and purchased a load of equipment from a friend — this included a purification system (pre filter, 2 RO's and 1 DI) along with some brushes, poles and tanks etc. 

Pretty much since we got the equipment we've been getting a TDS reading of around 30 or so coming out of the RO, obviously this takes it's toll on the resin filter and we've already had to replace the resin once as the TDS readings were getting too high. We've done the following and still we're getting readings of 25-30 coming out of the RO:

- Had Thames Water come up to give us a dedicated line to improve psi/flow

- Purchased a pump to increase PSI going into the pre-filter (we generally get about 120psi now)

- Replaced the membranes in the RO and replaced the pre-filter (we did this today as a last resort thinking it would solve the issue)

 

Yet still, we're getting readings of approx. 30 coming out of the RO and now it's started to creep up to 5-6 coming out of the DI so obviously the resin needs to be replaced again.

Does anyone know what the issue could be? As I said we're kind of at our wits end so any help would be much appreicated!

Cheers,

Ryan

As per @Apw1210. You need to flush a new membrane to remove the preservatives.

You need to give us more detail about your r/o and tap water tds.

I notice that you refer to your pre-filter (singular) and 2 membranes. I'm guessing that you have an old Merlin or its predecessor the PRF. 

 

 

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2 hours ago, Neil Mitchell said:

About what I get get another DI vessel connect it after the original one to get more life out your resin .

Wont that just prolong the resin for double but only because we have twice as much resin.....? 

1 hour ago, spruce said:

As per @Apw1210. You need to flush a new membrane to remove the preservatives.

You need to give us more detail about your r/o and tap water tds.

I notice that you refer to your pre-filter (singular) and 2 membranes. I'm guessing that you have an old Merlin or its predecessor the PRF. 

 

 

Thanks Spruce, we have 2 x axiom hf5 membranes after the pre filter, going into a 7l resin tank. 

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2 hours ago, Iron Giant said:

Sounds about normal for Thames Water in Surrey as I am guessing your tap tds before the R/O is over 250ppm 

Not when my colleague who sold the system to us in Sussex gets 280 and was getting below 9.

A reading of 30tds is extremely high for these filters and would only result in around 3000L of water for every 7L of resin.

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What size are the membranes?

How much pure are you trying to produce a day?

What tds are you getting from the waste outlet?

You have 'throttled' the waste output from your membranes haven't you? Not closed the waste but a little open?

On the spec sheets for the HF5 they seem to run them at 80psi even though they are rated at 400psi. No idea if 120psi is reducing efficiency or not?

I assume you are running the membranes in parallel so you can get more pure a day? Or are you running the waste out of one into the second membrane to reduce waste?

You did flush the pre filters before connecting to the membrane didn't you?

Edited by ched999uk
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7 hours ago, Ryan316 said:

Wont that just prolong the resin for double but only because we have twice as much resin.....? 

Thanks Spruce, we have 2 x axiom hf5 membranes after the pre filter, going into a 7l resin tank. 

Please send us some detailed photos of your r/o so we can see what you have an advise accordingly.

You need to sort out why your pure output is so bad before you start with double di resin vessels. Do a search for double di and see why it saves resin for people who don't use an r/o.

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Master Jedi Alejandro
7 hours ago, Ryan316 said:

Wont that just prolong the resin for double but only because we have twice as much resin.....? 

I don't use RO, DI only, but can answer this.

So basically, after you fill the second resin vessel then no, no extra resin used, it just prolongs the life of the new stuff, since the first vessel bringing it down further and the second vessel is finishing off. Once PPM out of the second start to creep up, simply swap them round and put new resin in the one that had been the first one (if that makes sense). You'll use less resin overtime this way.

Here's a (attempted) diagram:

RO - DI1 - DI2 - Tank

Then, when PPM starts to creep up, change the resin in DI1 and swap them over. So it's:

RO- DI2 - DI1 - Tank

Then repeat, forever, until the sun burns out. 😄

Hope that helps. I use two DIs myself. 

 

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doug atkinson

It could be that your R/O isn’t set up right. How long does it take a fill a litre jug with waste and pure.

Having a 120 PSI is a bit overkill as with an HF5 you just need 80psi when setting your ratio.

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If your membrane is new...flush, flush and flush some more. I've just recently changed mine and it needed hours...maybe at least 6-8 of flushing and quite a few fills of an 800l tank before it started to work as it should. I know the recommended is 2 ish. But in my experience, recommended and real world results was massively different!

  • Agree 1
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ShropsWindowCleaner

I have an old Merlin RO with new membranes and carbon block. My new membranes started at 50ppm and took 20 hours of flushing to achieve 11ppm. As has been mentioned, have you bedded in the new membranes?

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Thank you for the in depth replies! To clarify a couple of points/questions from everyone:

 

— we did indeed flush both the pre filter and the membranes. As per some specs we saw online we flushed the pre-filter for 30 mins and the membranes for approx. 20 mins.

However after taking the gear to the company we purchased the membranes from we've deduced the problem was with a faulty waste valve — after sorting that we're getting 13ppm out of the RO, with the DI taking us down to 0. We're pretty happy with that for now, thanks for all your help! 

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1 hour ago, Suhrly said:

If your membrane is new...flush, flush and flush some more. I've just recently changed mine and it needed hours...maybe at least 6-8 of flushing and quite a few fills of an 800l tank before it started to work as it should. I know the recommended is 2 ish. But in my experience, recommended and real world results was massively different!

I have never flushed a membrane for more than 15-30 muinits when new and always had a reading of 2-3 out if it and no issues , no idear why it’s nessasary to flush for so long ?..

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2 hours ago, Pjj said:

I have never flushed a membrane for more than 15-30 muinits when new and always had a reading of 2-3 out if it and no issues , no idear why it’s nessasary to flush for so long ?..

Me neither, but that's what happened to me. I made a new topic asking for any clues as to why with Spruce and Doug Atkinson chiming in but the only thing that (seemed) to solve it was just to wear it in for LOTS of hours 🤷‍♂️

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8 hours ago, Pjj said:

I have never flushed a membrane for more than 15-30 muinits when new and always had a reading of 2-3 out if it and no issues , no idear why it’s nessasary to flush for so long ?..

Could possibly be because your TDS is much lower. Not working at 98% with a starting TDS of below 100 isn't as bad as a TDS of 300+. If the membrane is working at 93% then your TDS would be around 7, mine would be around 30.

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doug atkinson
10 hours ago, Pjj said:

I have never flushed a membrane for more than 15-30 muinits when new and always had a reading of 2-3 out if it and no issues , no idear why it’s nessasary to flush for so long ?..

With the cheaper membranes they are made with a different membrane sheet so not much chemicals are added to protect the membrane sheet as it is not worth it.

The higher quality membrane sheet will have more chemicals on them and the shelf life will be 4 times more than the cheaper stuff you see.

So with the quality membrane sheet you need to flush longer.

With PRF membranes these are wet so no flushing needed but shelf life is very short.

 

 

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1 hour ago, doug atkinson said:

With the cheaper membranes they are made with a different membrane sheet so not much chemicals are added to protect the membrane sheet as it is not worth it.

The higher quality membrane sheet will have more chemicals on them and the shelf life will be 4 times more than the cheaper stuff you see.

So with the quality membrane sheet you need to flush longer.

With PRF membranes these are wet so no flushing needed but shelf life is very short.

 

 

Mine are film tech I never had any cloudy water when first fitting them and after 30-40 muinits had good water they are now 6 years old and still producing the same reading , we produce between 1000-2500 ltr per day with that van . 

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