TDS Creep Help
- Thread starter h2pvnus
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Velodog2
Well-Known Member
You are talking about the relatively high TDS output from the RO section when you begin to put water through it? I just plumbed a bypass to the waste line that I turn on for about 10 minutes when I start the unit up that dumps the RO output to keep the DI from being depleted too quickly.
pciscott
Active Member
Do you make up your water into a storage container? If yes the Tunze RO controller 8555 can be used to determine a high and low point to turn water off and on. I have a 130 gallon container and it will not turn on the RO until it is down 30 gallons. I used to have a float switch and the TDC creep would eat my DI fast.
I also found that Spectrapure 99 percent rejection membranes can save on DI as well. Also a soft water system added to my house changed my TDS from the 400 to 500 range down to 250 before my RODI. My 99 percent membrane knocks it to 2 to 3 TDS before it hits the DI. I still get a little creep, but the Tunze 8555 minimizes that. I have looked into a auto flush valve, and they do make them for commercial systems, but they are hard to find information on.
Good luck and here is a link to the tunze.
RO Water Controller - Tunze - Bulk Reef Supply
I also found that Spectrapure 99 percent rejection membranes can save on DI as well. Also a soft water system added to my house changed my TDS from the 400 to 500 range down to 250 before my RODI. My 99 percent membrane knocks it to 2 to 3 TDS before it hits the DI. I still get a little creep, but the Tunze 8555 minimizes that. I have looked into a auto flush valve, and they do make them for commercial systems, but they are hard to find information on.
Good luck and here is a link to the tunze.
RO Water Controller - Tunze - Bulk Reef Supply
TDS creep is an issue inherent with all membranes regardless of brand, size, "flush kits" or sediment and carbon filters sizes.
What happens is when you shut the system off there is tap water on the raw water side of the membrane and treated RO water on the other side of the membrane fabric. Since RO water is agressive, it is always trying to get back to its natural "dirty" state so attracts anything it can to get back in balance with nature. The tap water osmoses or travels through the membrane fabric until the TDS or contaminants in the tap water and RO water equalize.
When you start the system again, that initial spurt of water with the "TDS creep" or high TDS travels from the RO membrane to your DI resin causing it to exhaust faster than if it were treating straight RO water. Over time, depending on how often you make water the resin exhausts and needs replacement. If you were to make fewer, but longer filter runs or large batches the resin would last longer as you would have fewer TDS creep incidents versus if you make smaller, more frequent batches.
That is one way to extend the life of your DI.
Another is to install a DI bypass valve. This is not the same as a "flush kit" and does something completely different since the DI bypass is on the treated or RO side of the membrane and a flush kit is on the waste or brine side of the membrane. A DI bypass is as simple as a 1/4" John Guest style tee and a 1/4" ball valve installed between the RO and the DI which you open each time you start the system and flush a few ounces of TDS creep to the drain before the RO TDS drops to normal and you close the valve to make DI. A little more elaborate system would use a 3 way ball valve and even more elaborate are systems that automate this function.
DI has a limited capacity for TDS, usually between 3,000 and 6,000 total TDS per 16 oz of fresh DI resin. if you are sending a spurt of high TDS water to the resin every time you start the system it is going to exhaust quicker than if you flush the creep out for a minute or so and send only low TDS RO water to the resin.
"Flush kits" are located in the waste line of the RO system. When you open the valve to flush it usually bypasses the flow restrictor and increases the velocity, in theory scouring the tap water side of the membrane and cleaning it but again this is on the waste side, the TDS creep is already on the treated side so is not affected. In theory if you fushed the waste side BEFORE you shut the system off each time you use it it may slightly lower the TDS that is allowed to "creep" but it is minimal at best and how many owners know the proper way and time to use a flush kit? Most flush on start up and that does nothing, again since it is only flushing the waste side, not the treated side.
Water softeners do not lower TDS, in fact in most cases they actually raise the TDS slightly since the ion exchange bewteen sodium and calcium/magnesium is not an exact 1:1 ratio.
What happens is when you shut the system off there is tap water on the raw water side of the membrane and treated RO water on the other side of the membrane fabric. Since RO water is agressive, it is always trying to get back to its natural "dirty" state so attracts anything it can to get back in balance with nature. The tap water osmoses or travels through the membrane fabric until the TDS or contaminants in the tap water and RO water equalize.
When you start the system again, that initial spurt of water with the "TDS creep" or high TDS travels from the RO membrane to your DI resin causing it to exhaust faster than if it were treating straight RO water. Over time, depending on how often you make water the resin exhausts and needs replacement. If you were to make fewer, but longer filter runs or large batches the resin would last longer as you would have fewer TDS creep incidents versus if you make smaller, more frequent batches.
That is one way to extend the life of your DI.
Another is to install a DI bypass valve. This is not the same as a "flush kit" and does something completely different since the DI bypass is on the treated or RO side of the membrane and a flush kit is on the waste or brine side of the membrane. A DI bypass is as simple as a 1/4" John Guest style tee and a 1/4" ball valve installed between the RO and the DI which you open each time you start the system and flush a few ounces of TDS creep to the drain before the RO TDS drops to normal and you close the valve to make DI. A little more elaborate system would use a 3 way ball valve and even more elaborate are systems that automate this function.
DI has a limited capacity for TDS, usually between 3,000 and 6,000 total TDS per 16 oz of fresh DI resin. if you are sending a spurt of high TDS water to the resin every time you start the system it is going to exhaust quicker than if you flush the creep out for a minute or so and send only low TDS RO water to the resin.
"Flush kits" are located in the waste line of the RO system. When you open the valve to flush it usually bypasses the flow restrictor and increases the velocity, in theory scouring the tap water side of the membrane and cleaning it but again this is on the waste side, the TDS creep is already on the treated side so is not affected. In theory if you fushed the waste side BEFORE you shut the system off each time you use it it may slightly lower the TDS that is allowed to "creep" but it is minimal at best and how many owners know the proper way and time to use a flush kit? Most flush on start up and that does nothing, again since it is only flushing the waste side, not the treated side.
Water softeners do not lower TDS, in fact in most cases they actually raise the TDS slightly since the ion exchange bewteen sodium and calcium/magnesium is not an exact 1:1 ratio.
