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RO TDS question


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I’ve fairly recently bought a pumped RO system as I was fed up of the journey to spotless and wanted to produce my own water for less hassle.

It’s been working well but I’ve noticed the TDS is creeping up slightly after the DI cartridge that’s part of the system. I’ve not needed to produce much so far, probably about 400-500 litres.

It’s 200gpd and pumped as I have low water pressure (about 30psi). Tap TDS is around 250.

I’m very vigilant and have followed the instructions to the letter - including flushing before I start to fill and a bit afterwards aswell.

The problem is I don’t always need water, (small round which I’m trying to build up) so I’ve been producing and storing as I need it. I’m keeping my tank topped up, rather than letting it run out and filling from empty, but sometimes the RO doesn’t need to be used for a week or more, so it’s kept turned off and disconnected (I connect it to the garden tap as I don’t own the property so can’t connect it directly to the mains).

Could this be the reason the TDS has started to climb already?

I actually have two DI vessels which I was going to use instead (I know, the cost of resin), but thought the RO would work out cheaper. Just wondering as because the pure water I need is a bit more “as and when”/“on demand@ for me at present, would double DI be better for the time being?

Thanks for any advice you can give.

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I would run your R/O for 5-10 minutes every other day even when not needed otherwise you will need to flush the R/O for about 20 minutes or so if not used for a week,  over the years we have all gone on holiday and left ours standing for days or weeks so a longer flush is required before production, 

Also you say you have a DI but I am guessing its 10" cartridge the same size as the pre-filters so this could be the issue but you should still have managed to produce more than 4-500ltrs of pure before tds creep

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You need to tell us what the tds of the pure after r/o and before the di vessel is @wgwindows. Before you take this reading you must let the r/o run producing water for at least 5 minutes.

The higher this figure is the faster you will go through resin.

Ideally you need a figure of around 4 to 5 ppm.

Then you need to check the ratio between the pure you are producing and the waste you are sending to the drain. With that tap water tds your starting point should be around 60% waste to 40% pure and tweak from there.

After these checks you need to invest in a bigger di vessel. The 10" that is part of the unit isn't big enough. Something around 7 liters should do you. Try to go for a new one. There are a lot of refurbished units advertised that are botch jobs. Try not to get to involved with units already filled with resin. Rather, buy your own resin from a recognised wfp supplier and fill your own. You then know you aren't being screwed with a half filled vessel with a low grade resin for top dollar pricing.

 

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Thanks for the replies everyone. Yes I have two DI vessels already. I think a 7 and a 4 litre. The RO goes in a line of sediment, then carbon, then into the membrane, and then a little DI cartridge. I thought I might remove the cartridge, then just let it go through DI vessel and into the tank. Many thanks again.

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13 minutes ago, wgwindows said:

Thanks for the replies everyone. Yes I have two DI vessels already. I think a 7 and a 4 litre. The RO goes in a line of sediment, then carbon, then into the membrane, and then a little DI cartridge. I thought I might remove the cartridge, then just let it go through DI vessel and into the tank. Many thanks again.

You need to get the rejection rate sorted. If you don't you will eat through resin

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1 hour ago, spruce said:

You need to get the rejection rate sorted. If you don't you will eat through resin

Sorry I’m not sure what rejection rate means. After measuring I am on about a 40:60 ratio pure to waste. Before the resin the TDS through the RO is down from 247 (reading today) to 7.

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8 minutes ago, wgwindows said:

Sorry I’m not sure what rejection rate means. After measuring I am on about a 40:60 ratio pure to waste. Before the resin the TDS through the RO is down from 247 (reading today) to 7.

That's fine, your R/O is removing 97% and the waste to pure ratio is fine. I wonder if the resin you're using is either spent or rubbish.

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29 minutes ago, Part Timer said:

That's fine, your R/O is removing 97% and the waste to pure ratio is fine. I wonder if the resin you're using is either spent or rubbish.

Yes could be. It’s a little cartridge with I think only about 0.75 litres. I thought if it’s gone I’ll just take it out leave that bit of the housing empty - and let it run out and through my DI vessel instead 👍

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