RO/DI...need some help

Scudd · 06/11/2007, 01:14 PM

I just installed an RO unit last week. Its up and running, but before I use the water for the fish tank I wanted to test its quality.
I pick up a TDS meter from Buckeye Field Supply and recieved it today. My water from the RO tests at 001 to 002. When I test the water from the LFS it tests at 035, is this good or bad. Also, how can I test for Chloramines and other things?
Should I add the Deionization Canister tothe system?
Thanks any thoughts would help.

Travis L. Stevens · 06/11/2007, 01:28 PM

The lower the better. 1-2 is GREAT! Adding a DI unit will most likely drop it to Zero. You must have decent tap water. As far as your LFS goes, if it is testing at 35, then they are getting close to time to change their filters. It's not that bad though. People usually change their filters when it hits 50. Some people will change them at less of about 25, but they are either perfectionists or have a very specific aquarium

AZDesertRat · 06/11/2007, 01:41 PM

50 ? A normal 75 GPD RO membrane is capable of 96 to 98% removal or rejection so even if you have a tap water TDS of 1000, which is rare, you should be seeing an RO only TDS of 20 to 40 absolute worst case. My tap water TDS is 850 and with RO only I average less than 7 TDS. You really can't put a number like 25 or 50 to it without knowing what the tap water TDS is. The only thing you can say is it should be 96 to 98% less than whatever the starting TDS was.

50 to me would indicate poor maintenance of either the membranes or the holding vessel or both. Changing prefilters and carbons has little to no effect on final TDS, its the RO membrane and the DI resin that affect TDS. Pre and carbons are there to protect the membrane so it can do its job.

When it comes to RO/DI 2 or 3 final TDS is my absolute maximum. The maximum recommended final DI TDS is usually about 1/2 to 2/3 of what the RO only TDS is or you might as well be using RO only or even tap water. The thing to remember is once you start seeing anything other than 0 TDS out of the DI you are returning weakly ionized substances back into your treated water. Some weakly ionized substances are silicates and phosphates both of which can cause you problems.

Scudd · 06/11/2007, 01:45 PM

How long do these filters usally last? I know the membrane said 1-2 years.

AZDesertRat · 06/11/2007, 02:38 PM

Prefilters and carbons should be changed every 6 months. If you keep up with the regular filter changes and use good quality replacements a membrane should last 3+ years.

06/11/2007, 01:14 PM	#1
Scudd Registered Member Join Date: Nov 2003 Location: Largo, Florida Posts: 504	RO/DI...need some help I just installed an RO unit last week. Its up and running, but before I use the water for the fish tank I wanted to test its quality. I pick up a TDS meter from Buckeye Field Supply and recieved it today. My water from the RO tests at 001 to 002. When I test the water from the LFS it tests at 035, is this good or bad. Also, how can I test for Chloramines and other things? Should I add the Deionization Canister tothe system? Thanks any thoughts would help. __________________ "... I have seen that in any great undertaking it is not enough for a man to depend simply upon himself." Lone Man (Isna-la-wica) Teton Sioux. Current Tank Info: 92 Gallon Corner Reef

06/11/2007, 01:28 PM	#2
Travis L. Stevens Registered Member Join Date: Nov 2004 Location: Perry, OK Posts: 13,946	The lower the better. 1-2 is GREAT! Adding a DI unit will most likely drop it to Zero. You must have decent tap water. As far as your LFS goes, if it is testing at 35, then they are getting close to time to change their filters. It's not that bad though. People usually change their filters when it hits 50. Some people will change them at less of about 25, but they are either perfectionists or have a very specific aquarium __________________ Travis Stevens Current Tank Info: Restarting 28g Bowfront

06/11/2007, 01:45 PM	#4
Scudd Registered Member Join Date: Nov 2003 Location: Largo, Florida Posts: 504	How long do these filters usally last? I know the membrane said 1-2 years. __________________ "... I have seen that in any great undertaking it is not enough for a man to depend simply upon himself." Lone Man (Isna-la-wica) Teton Sioux. Current Tank Info: 92 Gallon Corner Reef

06/11/2007, 01:41 PM	#3
AZDesertRat Moved On Join Date: Jan 2002 Location: NW Phoenix Posts: 16,621	50 ? A normal 75 GPD RO membrane is capable of 96 to 98% removal or rejection so even if you have a tap water TDS of 1000, which is rare, you should be seeing an RO only TDS of 20 to 40 absolute worst case. My tap water TDS is 850 and with RO only I average less than 7 TDS. You really can't put a number like 25 or 50 to it without knowing what the tap water TDS is. The only thing you can say is it should be 96 to 98% less than whatever the starting TDS was. 50 to me would indicate poor maintenance of either the membranes or the holding vessel or both. Changing prefilters and carbons has little to no effect on final TDS, its the RO membrane and the DI resin that affect TDS. Pre and carbons are there to protect the membrane so it can do its job. When it comes to RO/DI 2 or 3 final TDS is my absolute maximum. The maximum recommended final DI TDS is usually about 1/2 to 2/3 of what the RO only TDS is or you might as well be using RO only or even tap water. The thing to remember is once you start seeing anything other than 0 TDS out of the DI you are returning weakly ionized substances back into your treated water. Some weakly ionized substances are silicates and phosphates both of which can cause you problems.

06/11/2007, 02:38 PM	#5
AZDesertRat Moved On Join Date: Jan 2002 Location: NW Phoenix Posts: 16,621	Prefilters and carbons should be changed every 6 months. If you keep up with the regular filter changes and use good quality replacements a membrane should last 3+ years.