How long till TDS hit 0

[Cubbies]

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

 

[caudill187]

Weird. I, like you, would expect it to be zero by now. What is your pressure at the RO membrane?

 

[gmoney243]

You should get 0 TDS imediately out of your DI. Where is this 40 tds commin from?

Sent from my Vortex using Tapatalk 2

 

[cdness]

Well there is a creep of TDS when first turning on the RODI for the day to make water. It will go down slowly to your normal rejection rate (if you are starting at 300 a 98% RO membrane rejection should come out around 6) after the RO part but shouldn't take more than 5 minutes. Now that water that does creep up should still come out of the DI at 0 TDS.

The carbon block and sediment filters will not have a major effect on TDS. They are in place to keep the larger particles and harmful chemicals off the RO membrane as they can damage that part. The Membrane takes the initial major filtration part and the DI is like a polisher.

What re you using to test the TDS? If it's an inline one you may want to try testing distilled water and see what that's at. It should be low, but I have had the inline meters be off by a few TDS before.

So to figure out more, try testing the water on the output side of the RO membrane right BEFORE it goes into the DI section. Take the TDS of the incoming tap water as well and compare the two numbers. Depending on your membrane you should show a number after the RO membrane that is between 2% and 5% of the incoming TDS.

Next test the water after the DI and see how much it drops. It should drop to 0, but if it doesn't the DI is probably bad. FYI you can't always trust the color change as it can get exhaused quicker than it changes. Use the TDS meters to know for sure.

 

[btkrausen]

Well there is a creep of TDS when first turning on the RODI for the day to make water. It will go down slowly to your normal rejection rate (if you are starting at 300 a 98% RO membrane rejection should come out around 6) after the RO part but shouldn't take more than 5 minutes. Now that water that does creep up should still come out of the DI at 0 TDS.

The carbon block and sediment filters will not have a major effect on TDS. They are in place to keep the larger particles and harmful chemicals off the RO membrane as they can damage that part. The Membrane takes the initial major filtration part and the DI is like a polisher.

What re you using to test the TDS? If it's an inline one you may want to try testing distilled water and see what that's at. It should be low, but I have had the inline meters be off by a few TDS before.

So to figure out more, try testing the water on the output side of the RO membrane right BEFORE it goes into the DI section. Take the TDS of the incoming tap water as well and compare the two numbers. Depending on your membrane you should show a number after the RO membrane that is between 2% and 5% of the incoming TDS.

Next test the water after the DI and see how much it drops. It should drop to 0, but if it doesn't the DI is probably bad. FYI you can't always trust the color change as it can get exhaused quicker than it changes. Use the TDS meters to know for sure.

Solid advice.

 

[AZDesertRat]

Sediment and carbon filters have very little to ABSOLUTELY NOTHING to do with TDS, their sole purpose is to protect the RO membrane which is the workhorse and removes 90 to 98% of the TDS and protects the DI resin which remeoves the rest. Changing sediment and carbon ONLY helps the membrane do its job, it does not lower TDS.
TDS or dissolved solids are in the 0.0001 micron range, dissolved in the tap water. Suspended solids are what the sediment and carbon remove, along with chlorine, and are in the 1 micron or large range in most cases which is why the sediment filter is like 1 micron, 0.5 microns, 5 mircrons etc. The smaller micron size the better so it protects the billions of tiny pores in the carbon block which should also be in the 0.5 or 0.6 micron range and an absolute rated filter is much better than a nominal rated filter.

What is your tap water TDS, RO only TDS before the DI and final RO/DI TDS? Those three numbers tell you where your problem lies.

Don't waste money on or rely on color changing DI resins, most are close to worthless and are not the least bit accurate. ALWAYS use and rely on your TDS meter and hopefully it is a handheldand not a dual inline which are ballpark at best.