How long till TDS hit 0

Cubbies · 05/25/2012, 06:56 AM

I changed out my sediment and carbon block filters last night on my RODI unit. It is only a 4 stage 50GPD unit, nothing huge. TDS was coming out a bit high so I double checked everything was in order. Everything checks out. I don't believe it's the membrane or the DI. The membrane is roughly 9 months and the DI I changed a couple months ago and color hasn't changed yet(it's color changing). My TDS out of tap comes out a bit under 300. When I first put the filters it was coming at around 350. It is now at about 40 but I ran it for 4 hours last night and it's been running for about 1/2 hr this morning. Is this normal. I don't believe it has happened to me before. I was wondering if maybe different filters do this or what. Do any of you run it for a bit before hitting 0? Thanks, Geno

shifty51008 · 05/25/2012, 08:36 AM

if your tap water is 300 and your getting 40 out of the membrane then I would suggest replacing the membrane, you should be getting less than 10 at the most, and with 40 going into the DI then that will kill your DI fast and it is probly shot also.

what is your water pressure going into the membrane?

I would also suggest switching the membrane to a 75gpd one and get a 75gpd flow restrictor also the 75 gpd membranes have a higher rejection rate than the 50gpd ones

Randy Holmes-Farley · 05/25/2012, 08:41 AM

Changing the sediment and carbon blocks won't noticeable change the TDS coming out.

Assuming the numbers are accurate, the DI is either not installed correctly, has large channels running through it, or is depleted.

jeff@zina.com · 05/25/2012, 10:28 AM

Yep. DI will take the TDS to 0 by itself. My guess is it may be as simple as the membrane got dislodged and needs to be reseated properly, otherwise water is bypassing it. Also, don't rely on color changes. Some resins change color too early, some too late. I have yet to see any change at the point when the DI is actually exhausted.

Jeff

KStatefan · 05/25/2012, 10:33 AM

As Randy said prefilters to not change the TDS readings.

What is the TDS coming out of the membrane?

05/25/2012, 06:56 AM	#1
Cubbies Registered Member Join Date: Jan 2011 Location: NW IL Posts: 1,475	How long till TDS hit 0 I changed out my sediment and carbon block filters last night on my RODI unit. It is only a 4 stage 50GPD unit, nothing huge. TDS was coming out a bit high so I double checked everything was in order. Everything checks out. I don't believe it's the membrane or the DI. The membrane is roughly 9 months and the DI I changed a couple months ago and color hasn't changed yet(it's color changing). My TDS out of tap comes out a bit under 300. When I first put the filters it was coming at around 350. It is now at about 40 but I ran it for 4 hours last night and it's been running for about 1/2 hr this morning. Is this normal. I don't believe it has happened to me before. I was wondering if maybe different filters do this or what. Do any of you run it for a bit before hitting 0? Thanks, Geno

05/25/2012, 08:36 AM	#2
shifty51008 12-5 Chiefs record Join Date: Mar 2010 Location: NW Iowa Posts: 10,134	if your tap water is 300 and your getting 40 out of the membrane then I would suggest replacing the membrane, you should be getting less than 10 at the most, and with 40 going into the DI then that will kill your DI fast and it is probly shot also. what is your water pressure going into the membrane? I would also suggest switching the membrane to a 75gpd one and get a 75gpd flow restrictor also the 75 gpd membranes have a higher rejection rate than the 50gpd ones __________________ 75 gal. mixed DT, 100 gal. sump, 50 gal. fuge, Clownfish breeder

05/25/2012, 08:41 AM	#3
Randy Holmes-Farley Reef Chemist Join Date: Apr 2001 Location: Arlington, Massachusetts Posts: 86,233	Changing the sediment and carbon blocks won't noticeable change the TDS coming out. Assuming the numbers are accurate, the DI is either not installed correctly, has large channels running through it, or is depleted. __________________ Randy Holmes-Farley Current Tank Info: 120 mixed reef

05/25/2012, 10:28 AM	#4
jeff@zina.com Registered Member Join Date: Apr 2010 Location: Naples, FL Posts: 3,345	Yep. DI will take the TDS to 0 by itself. My guess is it may be as simple as the membrane got dislodged and needs to be reseated properly, otherwise water is bypassing it. Also, don't rely on color changes. Some resins change color too early, some too late. I have yet to see any change at the point when the DI is actually exhausted. Jeff

05/25/2012, 10:33 AM	#5
KStatefan Registered Member Join Date: Aug 2010 Posts: 172	As Randy said prefilters to not change the TDS readings. What is the TDS coming out of the membrane?