[paul mather]

No 1

I am finding that after replacing the resin in my di unit, the TDS reading stays at 0 for only a couple of days & then steadily rises to 4 or 5, then levels off. WHY?
I have  a 200GPD Ro-man Ro unit. My water pressure is quite low at about 40psi, is that the problem?

No2

I have a friend who is pricing up his own system, he lives in Peterborough an area with very hard water. Is it worth the extra expense to install a water softener before his RO Unit.
I was told it will preserve his membrane, however if he buys a Ro-man ro unit a membrane only costs £26 to replace so is it worth the extra expense? Any comments please.

[Helen]

No1.
You need a booster pump to get the pressure somewhere around 65 psi
The tds entering the DI is clearly too high. A tds of 5 will last twice as long as 10 etc etc.
Ensure you flush the system on a daily basis

N02.
Depends how much water you are going to use. A decent water softener will cost lots so if he is going to get through 1,000s of litres of water per week it might make ecomnocic sense. But he will need to calculate the costs against each other first.
The RO Man system will work in very hard water areas provided the flush system is used on a regular basis.

[freshwater]

Paul

What is the TDS before your resin? Is you membrane on its way out? Always make a note of your TDS readings when the membrane is new for comparison later. Or it could be your resin is going off, OR you are getting channelling in the resin where the water just runs up the centre and does not come into contact with all the resin, do you use a vessel or a cartridge?

Hardwater: No it’s probably not worth it. BUT, there’s always a but, if you are on lowish pressure the TDS left in the water after the RO will most probably be hardness (calcium) which dries as hard water marks on glass. With softening the remaining TDS would be sodium, which is less likely to sick & harden on the glass.


steve@freshwatersystems.couk

[paul mather]

Paul

What is the TDS before your resin? Is you membrane on its way out? Always make a note of your TDS readings when the membrane is new for comparison later. Or it could be your resin is going off, OR you are getting channelling in the resin where the water just runs up the centre and does not come into contact with all the resin, do you use a vessel or a cartridge?

Hardwater: No it’s probably not worth it. BUT, there’s always a but, if you are on lowish pressure the TDS left in the water after the RO will most probably be hardness (calcium) which dries as hard water marks on glass. With softening the remaining TDS would be sodium, which is less likely to sick & harden on the glass.


steve@freshwatersystems.couk

I only have 2 TDS readings, one going into the unit & the other coming out, I don't know what the reading is after RO but before di, as the unit is self containded, water going in ranges from 175-215.

My Ro is no more than 2 months old so it can't be the membrane, is the Ro not working effeciently because of the low water pressure & therefore asking my di cannister to do too much?

[groundhog]

Have you tried phoning the RO man helpline, I had problems with my ro when I first got it, but I found RO man very helpful indeed.

[freshwater]

Paul,

If you do have low pressure you will get a high level of tds after the membrane, this will use up your resin more quickly. This is all basic numbers but at 200ppm on the way in, and low pressure you might get 90% reduction, leaving 20ppm on the way out. If you have a small cartridge of resin, sat one litre you can expect it to remove 50,000 ppm. So with water at 20ppm this is equiv. to 2500 litres before the resin is consumed. If this is the case you have to decide "do I spend on resin or do I spend on a pump". I would buy a pump.

steve@freshwatersystems.co.uk

[JM123]

freshwater I think you need to work on your Maths.

20ppm out will mean you will get 1000ltrs from 1 litre of resin (500,000/25 = 20,000:20,000/20ppm = 1000ltrs)

20ppm out of an RO is unacceptable, really you do want higher pressure but I wouldn't accept this from my RO (merlin at 48psi, tds between 300 and 350ppm - output 2000ltrs per day @4ppm.)

If a merlin can do it then why not an RO-MAN unit - I honestly think the ro-man units are poor, very low output and low quality.  Some may not like what I say but I'm voicing an honest opinion.  We used to use and supply aquafx units - low output (200+300gpd) but the quality is exceptional (water out of ro more often than not was between 0 and 1ppm from an inlet of 300 to 350ppm and low (48psi) pressure).

I'll say it again, if you are looking to buy a new RO choose carefully, AquaFX/Merlin/Desal get my vote.

[paul mather]

Paul,

If you do have low pressure you will get a high level of tds after the membrane, this will use up your resin more quickly. This is all basic numbers but at 200ppm on the way in, and low pressure you might get 90% reduction, leaving 20ppm on the way out. If you have a small cartridge of resin, sat one litre you can expect it to remove 50,000 ppm. So with water at 20ppm this is equiv. to 2500 litres before the resin is consumed. If this is the case you have to decide "do I spend on resin or do I spend on a pump". I would buy a pump.

steve@freshwatersystems.co.uk

I have ordered a pump, there is a delay of a week, so I guess in a weeks time I will have the answer myself.

I don't suppose it's too big an issue , I have regularly used water with a TDS reading of 5 or 6 & the results are fine, but it's just annoying me why I can only get very low readings for a very small period of time. Your theory on the low pressure causing the problem rings true, lets hope you are right.

[freshwater]

the maths are OK 50,000/20=2500, the starting point may differ. I always err on the high side eg 50,000 and not 20,000 per litre, as you know its very difficult with basic info to may a precise determination, and from experience resins always seem to last longer in the real world. BUT I do agree that from what I have heard ROmans ROs do not have the best output.

I have never tried Aquafx so I can not comment, personally I think the Merlin is not as good as its cracked up to be, but I do agree that Desal membranes are OK.



steve@freshwatersystems.co.uk

[groundhog]

Obviously my advice was too simple for you! ROMan know what there talking so ring them, easy problem solved!

[master cleaner]

Paul how big is your resin vessil i used the small one that comes with the 200gpd and it only lasted me a week i have since put a 2 ltr vessel on it and the resin lasts me 6 months , my water pressure is 40-45 psi so that isnt the problem and my tds is 250-300 it goes into the di at 013
all in all i am very happy with the 200gpd

gary

[paul mather]

Gary,

It is only 250ml capacity.

[Extremeclean]

Please dont be offended Paul but a DI vessel of 250ml on a 200 GPD unit is really too small. You will get fed up refilling it every few days even if the RO is working well.

It will last a bit longer when you get your pump but I would suggest a 700ml one as the minimum practical size. You will probably have to refill the 700 ml every 2 to 3 weeks but its got to be a lot better than the 250 ml one.

I hope the pump works out for you.  It should.

[freshwater]

Good point extreme

We always prefer a 18 x 17 vessel so you can have at least 10 litres of resin, the wider an longer bed (shape of the vessele) also mean you use more of the resin to its full capacity.

steve@freshwatersystems.co.uk

[freshwater]

CORRECTION

should have read 8 x 17

[paul mather]

Please dont be offended Paul but a DI vessel of 250ml on a 200 GPD unit is really too small. You will get fed up refilling it every few days even if the RO is working well.

It will last a bit longer when you get your pump but I would suggest a 700ml one as the minimum practical size. You will probably have to refill the 700 ml every 2 to 3 weeks but its got to be a lot better than the 250 ml one.

I hope the pump works out for you. It should.

I'm not offended in the slightest, the size of the DI vessel wasn't my choice, I just left everything up to Gardeners. Is that the reason why my Resin isn't lasting then, I'm expecting too much of such a small amount?