rodi tds measurement
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Anything other than zero is when I change mine.
The sediment and carbon block filters have very little to absolutely nothing to do with TDS, it is the RO membrane that removes 90-98% of the TDS and the DI that removes the remaining TDS. TDS is dissolved solids, tiny microscopic stuff in the 0.0001 micron range, sediment and carbon block filters are in the 0.5 to 10 micron range, thousands of times larger than TDS. The sole purpose of the sediment filter is to protect the billions of tiny pores in the carbon where chlorine is adsorbed and the carbons purpose is to protect the RO membrane from chlorine so it can remove TDS. You replace the sediment and carbon at 6 month intervals or if you are using a pressure gauge to monitor headloss through the filters and a low range chlorine test kit to monitor for chlorine breakthru you might be able to extend that but 6 months is an easy number to remember. Be sure to disinfect the system when you replace the sediment and carbon block filters.
The sediment and carbon block filters have very little to absolutely nothing to do with TDS, it is the RO membrane that removes 90-98% of the TDS and the DI that removes the remaining TDS. TDS is dissolved solids, tiny microscopic stuff in the 0.0001 micron range, sediment and carbon block filters are in the 0.5 to 10 micron range, thousands of times larger than TDS. The sole purpose of the sediment filter is to protect the billions of tiny pores in the carbon where chlorine is adsorbed and the carbons purpose is to protect the RO membrane from chlorine so it can remove TDS. You replace the sediment and carbon at 6 month intervals or if you are using a pressure gauge to monitor headloss through the filters and a low range chlorine test kit to monitor for chlorine breakthru you might be able to extend that but 6 months is an easy number to remember. Be sure to disinfect the system when you replace the sediment and carbon block filters.
Randy Holmes-Farley
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When the DI first starts to deplete, the product water coming out can actually have higher ammonia and phosphate than the incoming tap water since those are weakly bound and can those that have collected in the DI can be popped off by incoming sodium, chloride, etc.
I also suggest changing at 1, but if you have two in series, the first one can be run until it is removing almost nothing (little drop in TDS) to get the most out of it.
I also suggest changing at 1, but if you have two in series, the first one can be run until it is removing almost nothing (little drop in TDS) to get the most out of it.
Windy
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I would like some idea of the level of tds being processed by you guys. I am running 23 from the tap and 0 after the RO and have not changed a filter in more than a year. Your every six months must be based on some sort of TDS input level.
Robertchrisroph
Active Member
Numbers I have 170 tds coming out of tap checked with a meter. I just changed my di due to I had 1 tds coming out on the end and it was light brown (color changing). Started blue. I'm back to having 0 again
Windy, sounds like you are using an inline TDS meter and I question the 0 TDS after RO only. Since an RO membrane is only a 90 to 98% efficient devices it is impossible to have a true 0 TDS with RO only. Inlines are not as accurate as handhelds since they are not truly temperature compensated so it may indicate 0 but that is not a true reading due to the level of accuracy of the meter.
My softened tap water TDS averages around 560 right now, the RO only takes it to between 2 and 3 with a booster pump set at 95-100 psi and using a COM-100 handheld TDS meter. The dual DI's are both 0 and when the first starts showing 1 TDS I change the cartridge. If I used the same resin in both DI filters I would swap the second DI into the first and add a new cartridge in the #2 position but I use different resins so the first gets swapped about 3 times before I need to replace the second DI. I do not use or recommend color changing resins as most can be very unreliable, you are usually passing weakly ionized substances before it turns color.
My softened tap water TDS averages around 560 right now, the RO only takes it to between 2 and 3 with a booster pump set at 95-100 psi and using a COM-100 handheld TDS meter. The dual DI's are both 0 and when the first starts showing 1 TDS I change the cartridge. If I used the same resin in both DI filters I would swap the second DI into the first and add a new cartridge in the #2 position but I use different resins so the first gets swapped about 3 times before I need to replace the second DI. I do not use or recommend color changing resins as most can be very unreliable, you are usually passing weakly ionized substances before it turns color.
Randy Holmes-Farley
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I agree that it may be due to inaccuracy, but 98% rejection of 23 ppm input water should correctly read 0 ppm.
