RODI unit problem.

[20 gallon nano]

I got a 6 stage Watergeneral rodi system that I'm having issues with. Every time I start filling my container it would read 3 and then I would dump the water and start filling again and it would read 2 and then I do the same thing and it reads 1, eventually it goes down to zero and my whole 5 gallon container fills up with zero tds reading. Is there an explanation for this, why won't it read zezo in the first place? I had the unit for only couple months now so the filter are almost new.

 

[TheEngineer]

That's normal operation. It takes some time for the membrane to settle in and work at its peak. I wouldn't expect it to take more than a few minutes to get there though.

This is why a lot of people will only make a large batch at a time, you get better water quality.

 

[TheEngineer]

Oh, and I should add that I use a Water General system too. I've had it for 8 years with no issues.

 

[Harold Green]

They sell a diverter valve that you can put in between the membrane and the di cartridges so you can drain off the first high tds water until the membrane reaches the best numbers it's capable of. No really feasible for those of us using a float switch in a reservoir of ro water to control the ro filter.

 

[20 gallon nano]

They sell a diverter valve that you can put in between the membrane and the di cartridges so you can drain off the first high tds water until the membrane reaches the best numbers it's capable of. No really feasible for those of us using a float switch in a reservoir of ro water to control the ro filter.

How long does it take you to get it down to 0 dts? I keep draining it for almost an hour until its finally down from 1.

 

[Harold Green]

It takes about 3 to 5 minutes for the membrane to reach it's lowest tds then another minute or two to push through the di to the reservoir at 0 tds. I am running about 75psi so the pressure will make some difference along with the tds of your supply water. Regardless you should be getting 0 tds from your di output in a short while unless your resin is depleted or your water contains something that's difficult to remove, neither or which sounds like your issue. Try a valve to bypass the di until the membrane is flushed out. Remember each time you shut off the system high tds water will bleed back through the membrane and have to be flushed out again.

 

[AZDesertRat]

Lets troubleshoot your system.
What is your tap water TDS, RO only TDS before the DI and your final RO/DI TDS? What is your water pressure and water temperature? What is your exact measured waste ratio? Are you using a drinking water type pressure tank? Try making RO/DI with the tank disconnected as it stores TDS creep. Are you using the post RO/DI granular activated carbon taste and odor filter? If so try making water without it as it actually adds TDS to the water as the carbon degrades.

All RO membranes suffer from what is called TDS creep, it is caused when the water is sitting still and the agressive RO water on the treated side of the membrane causes the untreated tap water to osmose or pass through the membrane until the TDS equalizes. This first bit of water then passes to the DI resin when you first start making treated water until it gradually tapers off. This is a nuisance since it exhausts the DI much faster than normal. If you have a pressure tank it is even worse since the tank stores and accumulates that TDS creep which gets higher and higher unless the pressure tank is completely drained every day or two.

There are ways to help this situation. One is to install a DI bypass valve so you can manually flush the TDS creep to the drain each time you start the system but this is manual and if you have a pressure tank you will not be around every time the system cycles off and on to replenish the pressure tank. Another is to install a small 1/4" check valve between the RO membrane/pressure tank and the DI filter so you have RO only water in the tank for drinking and cooking but the DI is made directly from the RO membrane, not the storage tank so TDS creep is not an issue.
Follow this diagram for the check valve:
http://spectrapure.com/huds/4-STAGE-DWK-RODI-NAG.pdf

For the DI bypass valve it is as simple as installing a 1/4" tee between the RO membrane and the DI filter with a 1/4" ball valve on the outlet so you can open this valve and waste the first quart or so of TDS creep water to the drain before closing it and making RO/DI water.

With Water General/Filters Direct systems it is common to never see 0 TDS in the treated wate rdue to their inefficient horizontal DI tubes which short circuit and channel so the water takes the path of least resistance along the bottom and out where a reef quality RO/DI has a vertical 20 oz DI that fills from the bottom and exits the top so all resin and water come into contact with each other. You can help this situation by disconnecting the little horizontal tubes and mounting them vertically on the wall of a bracket so the fill from the bottom and exit the top of each one for better contact time. The other is to properly pack the resin by filling the tube, tapping it vertically on the table or counter top, refill, tap down again and so on until no more resin can be added and they are tightly packed with no voids or cavities. Resin actuall shrinks as it is used.

 

[20 gallon nano]

Lets troubleshoot your system.
What is your tap water TDS, RO only TDS before the DI and your final RO/DI TDS? What is your water pressure and water temperature? What is your exact measured waste ratio? Are you using a drinking water type pressure tank? Try making RO/DI with the tank disconnected as it stores TDS creep. Are you using the post RO/DI granular activated carbon taste and odor filter? If so try making water without it as it actually adds TDS to the water as the carbon degrades.

All RO membranes suffer from what is called TDS creep, it is caused when the water is sitting still and the agressive RO water on the treated side of the membrane causes the untreated tap water to osmose or pass through the membrane until the TDS equalizes. This first bit of water then passes to the DI resin when you first start making treated water until it gradually tapers off. This is a nuisance since it exhausts the DI much faster than normal. If you have a pressure tank it is even worse since the tank stores and accumulates that TDS creep which gets higher and higher unless the pressure tank is completely drained every day or two.

There are ways to help this situation. One is to install a DI bypass valve so you can manually flush the TDS creep to the drain each time you start the system but this is manual and if you have a pressure tank you will not be around every time the system cycles off and on to replenish the pressure tank. Another is to install a small 1/4" check valve between the RO membrane/pressure tank and the DI filter so you have RO only water in the tank for drinking and cooking but the DI is made directly from the RO membrane, not the storage tank so TDS creep is not an issue.
Follow this diagram for the check valve:
http://spectrapure.com/huds/4-STAGE-DWK-RODI-NAG.pdf

For the DI bypass valve it is as simple as installing a 1/4" tee between the RO membrane and the DI filter with a 1/4" ball valve on the outlet so you can open this valve and waste the first quart or so of TDS creep water to the drain before closing it and making RO/DI water.

With Water General/Filters Direct systems it is common to never see 0 TDS in the treated wate rdue to their inefficient horizontal DI tubes which short circuit and channel so the water takes the path of least resistance along the bottom and out where a reef quality RO/DI has a vertical 20 oz DI that fills from the bottom and exits the top so all resin and water come into contact with each other. You can help this situation by disconnecting the little horizontal tubes and mounting them vertically on the wall of a bracket so the fill from the bottom and exit the top of each one for better contact time. The other is to properly pack the resin by filling the tube, tapping it vertically on the table or counter top, refill, tap down again and so on until no more resin can be added and they are tightly packed with no voids or cavities. Resin actuall shrinks as it is used.

I shut off my resevoir when I'm filling my containers. I'm not able to check my tds pre membrain because I only have a hand held tds meter. That's very useful information about setting up the filters verticle, would I set up all of them verticle or only the di one?

 

[AZDesertRat]

A handheld TDS meter is the best kind to have and easiest to test all the different points with. First get yourself a squeaky clean clear glass drinking water glass washed by hand in extremely hot water so it has no dishwasher soap residue or antispotting rinses on it to interfere with TDS readings. Draw a glass of tap water and insert the meter, let it sit until the reading stabilizes, write it down then triple rinse the meter and glass in good RO/DI or distilled water. Disconnect the line between the RO membrane and the DI filter, fill the glass enough to get a good reading and repeat the above. After the triple rinse draw a sample of the RO/DI directly from the DI filter, insert the meter and do the above. What are your three TDS readings?