RO questions

[maroun.c]

Can you please post your TDS value after the RO?
at which level would it be time to change the membrane and how much maximum TDS would still be OK to go in DI?
My RO membrane is only 6 months old and was flitering 245 TDS water (from tap) to 30-35. Just tested it yesterday and TDSwas 120. Changed the pre filter (was there for 4 months and looked dark yellow) and Carbon , fidled with the waste water controller (which should affect TDS) for 1 hour and only got it down t 100 TDS. Do you think that the exhausted pre filter ended up clogging the RO membrane should I change it aready before hooking my new DI
thanks for any input.

[PRDubois]

I get 0

[maroun.c]

Before DI?

[jener8tionx]

70-100 ppm into unit
0 before di
0 after di

[Randy Holmes-Farley]

A typical RO membrane will drop TDS by 90-98%, depending on the exact membrane and what exactly in is the water. I discuss it here:

Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria
http://reefkeeping.com/issues/2005-05/rhf/index.htm

from it:

If you are evaluating an existing RO membrane and can collect water from the tap and after the RO membrane, the conductivity (in mS/cm or ppm TDS) should drop by a factor of more than 10 across it (to as much as 100), relative to the tap’s water. If the drop is less than a factor of 10, it is not working properly, and may have holes in it.

Monitor the DI resins by measuring the effluent’s conductivity, either with an inline meter (set to its most sensitive level), or by measuring the effluent manually. If you are using a TDS or conductivity meter, then the measured value should drop to near zero, or maybe 0-1 ppm TDS or 0-1 mS/cm. Higher values indicate that something is not functioning properly, or that the DI resin is becoming saturated and needs replacement. That does not necessarily mean, however, that 2 ppm TDS water is not OK to use. But beware that the flow of impurities and the conductivity may begin to rise fairly sharply when the resin becomes saturated. Do not agonize over 1 ppm versus zero ppm. While pure water has a TDS well below 1 ppm, uncertainties from carbon dioxide in the air (which gets into the water and ionizes to provide some conductivity; about 0.7 mS/cm for saturation with normal levels of CO2, possibly higher indoors) and the conductivity/TDS meter itself may yield results of 1 or 2 ppm even from totally pure water by not being exactly zeroed properly. Also note that the first impurities to leave the DI resin as it becomes saturated may be things that you are particularly concerned with (such as ammonia if your water supply uses chloramine or silica if there is a lot in the source water).

[maroun.c]

Thanks for the detailed info.
Guess I willchange my RO membrane. Would you suggest adding another RO membrane to the existing one as it's only 6 months old and dropping the TDS from 245 to 100 or would that decrease the pressure on the following membrane?

[S_Stoney_S]

200 odd before -> 0 after in mine. It is brand new however only done about 300g.

[Randy Holmes-Farley]

200 odd before -> 0 after in mine. It is brand new however only done about 300g.

Not after RO only. That must be after RO/DI? :)

[Randy Holmes-Farley]

Guess I willchange my RO membrane. Would you suggest adding another RO membrane to the existing one as it's only 6 months old and dropping the TDS from 245 to 100 or would that decrease the pressure on the following membrane?

I've not heard of using two is series and I'm not sure how you'd do it easily, pressure and waste wise.

[crvz]

<a href=showthread.php?s=&postid=14702513#post14702513 target=_blank>Originally posted</a> by maroun.c
Thanks for the detailed info.
Guess I willchange my RO membrane. Would you suggest adding another RO membrane to the existing one as it's only 6 months old and dropping the TDS from 245 to 100 or would that decrease the pressure on the following membrane?

I wouldnt bother trying to run a pair in series, I don't see what that would really help. At that TDS level, the membrane should last a good couple years, so I'm surprised that yours has stopped performing. Have you looked into other problems, such as bad pressure, frequent on/off cycling, or warm water into the RO setup? Those can ruin a membrane rather quickly.

[maroun.c]

No warm water and so far no other issues except that when I took the membrane out for inspection I found some yellowish water aroud it that probably has passed through the very dirty sediment and carbon filter that I just replaced. I'm assuming after readingRandy's article that this might have affected the membrane.

[maroun.c]

changed the membrane and TDs immediately dropped to 15. anyway pressure from the tap is around 40-60 PSA any idea if I need to add a pressure pump or maybe close down the valve to decrease the pressure? the membrane I bought had no optimal pressure printed on it. it's a 50 GPD GE membrane.

[Randy Holmes-Farley]

That pressure is fine. :)