RO/DI Question

pmcustom · 10/08/2006, 10:21 PM

My RO is putting out 70ppm...I haven't checked the source water, but shouldn't the output be a lot lower than that? The DI (I just added it) is dropping it to 50ppm...is that about all you can expect out of a DI? Does this mean my membrane is bad? Thanks.

kau_cinta_ku · 10/08/2006, 11:14 PM

how old are the filters and membraine? filters should be replaced every 6 monthes, membrane should be replaced 2-3 years and DI should be replaced when TDS starts to rise(rise up to 5ppm for most ppl) if any of your filters are past that age i suggest replaceing them. but it does look like your membrane is shot

pmcustom · 10/09/2006, 12:05 AM

i must have waited too long to change them...i have a new membrane on the way, though. thanks

drummereef · 10/09/2006, 12:12 AM

Your tds after the DI stage should be 0. The new membranes are a must. Randy told me never to put water in the tank with a tds above 1ppm. So, I heed his advice.

AZDesertRat · 10/09/2006, 08:10 AM

You probably let the carbon filter go too long and chlorine made it through and killed the membrane.
Always use a good quality Chlorine Guzzler type carbon block filter in a 1 or 0.6 or 0.5 micron size, not granular carbon of blocks with micron ratings above 1. The difference in chlorine capacity is tremendous, up to 20,000 gallons vs maybe 500 to 1000.
Also I hope you ordered a 75 GPD Dow Filmtec RO membrane as they are the best for our application.
Remember to always change the pre and carbon filters every 6 months even if you are using top of the line filters which you should be.

pmcustom · 10/09/2006, 10:59 AM

I just put on a new Chlorine Guzzler .6 micron carbon from BFS, and a Filmtec 75gpd membrane is on the way. Thanks.

Buckeye Hydro · 10/11/2006, 04:41 AM

Quote:

Originally posted by pmcustom
My RO is putting out 70ppm...I haven't checked the source water, but shouldn't the output be a lot lower than that? The DI (I just added it) is dropping it to 50ppm...is that about all you can expect out of a DI? Does this mean my membrane is bad? Thanks.

Remember that you want to monitor the tds readings in 3 locations: Tap water; after RO/before DI; and after DI.

That will allow you to monitor the perfromace of your membrane, and the performance of your DI resin.

Russ @ BFS

pmcustom · 10/11/2006, 04:48 AM

Is it safe enough to assume that the city water supply will stay basically the same and just monitor the RO output and the DI output? I would think as long as the RO output doesn't rise abnormally, then the membrane is okay. Thanks.

Buckeye Hydro · 10/11/2006, 05:03 AM

Supply water tds commonly fluctuate. Under normal conditions you could monitor just after the RO and after the DI. If trouble arises, I'd check in all three places.

Russ @ BFS

AZDesertRat · 10/11/2006, 08:18 AM

Tap water can and does change daily if not hourly. Changes in sources, blends, lake or impoundment levels, storm events and resulting high turbidity, treatment techniques, chemical feeds etc. Never assume what you have today you will have tomorrow.

pmcustom · 10/11/2006, 08:38 AM

that may be the case, but my point is that it doesn't matter much. as long as the RO output TDS stays relatively constant and does not rise substantially, then it's safe to assume that the membrane is doing its job and isn't damaged. that's what started this whole thread, my RO membrane being shot.

AZDesertRat · 10/11/2006, 08:53 AM

But the output does not remain constant. If the incoming TDS rises the RO product water also rises. It will vary significantly. My tap varies from 500 to over 1000 at times, granted that is a little extreme but it is not uncommon. At 98% rejection 500 TDS tap water the RO output would be 10, but at 1000 the RO is 20.
You can figure that DI life will go down by a huge factor. Every 2% increase in RO efficiency doubles the life of DI resin. A TDS of 10 going into a single mixed bed 24oz cartridge will yield about 250 to 300 gallons of good water, a TDS of 20 will only get you 125 to 150 gallons with the same resin. Its important to watch your RO efficiency as resin costs can eat you up pretty quickly.

pmcustom · 10/11/2006, 09:20 AM

i understand your point, but either way, i cannot change the supply water. all i care about is knowing if/when there is a problem with the RO. the supply tds might change all the time, but all i care about is if it's getting filtered properly. thanks for the info though, i didn't realize it would change that much.

AZDesertRat · 10/11/2006, 12:56 PM

As the RO membrane ages the TDS will rise. You will not know this unless you test regularly. Your only injdication is going to be premature failure or shortened life of the DI resin and again you will not know that unless you test it also or you wait until you see problems in your reef. Regular testing is the best option you have. It costs you nothing but a little time and it will save you money by catching things before they go bad.

10/08/2006, 10:21 PM	#1
pmcustom Registered Member Join Date: Oct 2003 Location: Columbus, Ohio Posts: 569	RO/DI Question My RO is putting out 70ppm...I haven't checked the source water, but shouldn't the output be a lot lower than that? The DI (I just added it) is dropping it to 50ppm...is that about all you can expect out of a DI? Does this mean my membrane is bad? Thanks.

10/09/2006, 12:12 AM	#4
drummereef Team RC Member Join Date: Jul 2006 Location: STL Posts: 14,754	Your tds after the DI stage should be 0. The new membranes are a must. Randy told me never to put water in the tank with a tds above 1ppm. So, I heed his advice. __________________ -Brett 180g Marineland Starfire In-Wall 278 gallon system

10/08/2006, 11:14 PM	#2
kau_cinta_ku Moved On Join Date: May 2005 Location: NW Iowa Posts: 8,669	how old are the filters and membraine? filters should be replaced every 6 monthes, membrane should be replaced 2-3 years and DI should be replaced when TDS starts to rise(rise up to 5ppm for most ppl) if any of your filters are past that age i suggest replaceing them. but it does look like your membrane is shot

10/09/2006, 12:05 AM	#3
pmcustom Registered Member Join Date: Oct 2003 Location: Columbus, Ohio Posts: 569	i must have waited too long to change them...i have a new membrane on the way, though. thanks

10/09/2006, 08:10 AM	#5
AZDesertRat Moved On Join Date: Jan 2002 Location: NW Phoenix Posts: 16,621	You probably let the carbon filter go too long and chlorine made it through and killed the membrane. Always use a good quality Chlorine Guzzler type carbon block filter in a 1 or 0.6 or 0.5 micron size, not granular carbon of blocks with micron ratings above 1. The difference in chlorine capacity is tremendous, up to 20,000 gallons vs maybe 500 to 1000. Also I hope you ordered a 75 GPD Dow Filmtec RO membrane as they are the best for our application. Remember to always change the pre and carbon filters every 6 months even if you are using top of the line filters which you should be.

10/09/2006, 10:59 AM	#6
pmcustom Registered Member Join Date: Oct 2003 Location: Columbus, Ohio Posts: 569	I just put on a new Chlorine Guzzler .6 micron carbon from BFS, and a Filmtec 75gpd membrane is on the way. Thanks.

10/11/2006, 04:48 AM	#8
pmcustom Registered Member Join Date: Oct 2003 Location: Columbus, Ohio Posts: 569	Is it safe enough to assume that the city water supply will stay basically the same and just monitor the RO output and the DI output? I would think as long as the RO output doesn't rise abnormally, then the membrane is okay. Thanks.

10/11/2006, 05:03 AM	#9
Buckeye Hydro .Registered Member Join Date: Sep 2006 Location: Cincinnati, Ohio Posts: 4,857	Supply water tds commonly fluctuate. Under normal conditions you could monitor just after the RO and after the DI. If trouble arises, I'd check in all three places. Russ @ BFS

10/11/2006, 08:18 AM	#10
AZDesertRat Moved On Join Date: Jan 2002 Location: NW Phoenix Posts: 16,621	Tap water can and does change daily if not hourly. Changes in sources, blends, lake or impoundment levels, storm events and resulting high turbidity, treatment techniques, chemical feeds etc. Never assume what you have today you will have tomorrow.

10/11/2006, 08:38 AM	#11
pmcustom Registered Member Join Date: Oct 2003 Location: Columbus, Ohio Posts: 569	that may be the case, but my point is that it doesn't matter much. as long as the RO output TDS stays relatively constant and does not rise substantially, then it's safe to assume that the membrane is doing its job and isn't damaged. that's what started this whole thread, my RO membrane being shot.

10/11/2006, 08:53 AM	#12
AZDesertRat Moved On Join Date: Jan 2002 Location: NW Phoenix Posts: 16,621	But the output does not remain constant. If the incoming TDS rises the RO product water also rises. It will vary significantly. My tap varies from 500 to over 1000 at times, granted that is a little extreme but it is not uncommon. At 98% rejection 500 TDS tap water the RO output would be 10, but at 1000 the RO is 20. You can figure that DI life will go down by a huge factor. Every 2% increase in RO efficiency doubles the life of DI resin. A TDS of 10 going into a single mixed bed 24oz cartridge will yield about 250 to 300 gallons of good water, a TDS of 20 will only get you 125 to 150 gallons with the same resin. Its important to watch your RO efficiency as resin costs can eat you up pretty quickly.

10/11/2006, 09:20 AM	#13
pmcustom Registered Member Join Date: Oct 2003 Location: Columbus, Ohio Posts: 569	i understand your point, but either way, i cannot change the supply water. all i care about is knowing if/when there is a problem with the RO. the supply tds might change all the time, but all i care about is if it's getting filtered properly. thanks for the info though, i didn't realize it would change that much.

10/11/2006, 12:56 PM	#14
AZDesertRat Moved On Join Date: Jan 2002 Location: NW Phoenix Posts: 16,621	As the RO membrane ages the TDS will rise. You will not know this unless you test regularly. Your only injdication is going to be premature failure or shortened life of the DI resin and again you will not know that unless you test it also or you wait until you see problems in your reef. Regular testing is the best option you have. It costs you nothing but a little time and it will save you money by catching things before they go bad.