RO/DI question

[AlexKilpatrick]

My RO/DI was way overdue for filter replacement. I measured the output at about 250. I replaced all three of the filters (sediment, carbon, DI) and then measured the output with a TDS meter. It was down to 0, so I thought everything was cool.

However, a week later, after running about 20 gallons, it is back up to 250 or so. I initially thought the TDS meter might be bad, so I bought some RO water from the store, and it measured at 4.

It seems like my only option now is to replace the membrane. However, I always thought that membranes went bad by just restricting output, not by producing bad water. Is thet wrong?

Any ideas or suggestions are appreciated.

[JimD]

Sounds like your RO membrane might have gone south on ya, Test the tds of the RO output to be sure, it should be in the 10/25 range.

[BuckeyeHydro]

However, I always thought that membranes went bad by just restricting output, not by producing bad water. Is thet wrong?

Any ideas or suggestions are appreciated.

The two typical indications your membrane has gone bad are reduced rejection rate, and reduced output.

Use your tds meter to compare the tap water tdds top the post -RO (pre-DI) numbers. Depending upon what membrane you have, you should see rejection rates of 90%+

Russ @ BFS

[OldSalty]

Your membraine is deffinatly GONE. What has happened, is it now has holes in it. It is VERY VERY inportant to change the carbon filters. In fact I've added an extra one. I've gone thru 3 membraines in less than 3 years, so I've learned the hard $$$$ way. You should also get a chlorene test kit and test to make sure there is none comming in to the membraine. If there is, the filters of course need to be changed. If you don't change them, the chlorene will eat up the membraine.

Just my 2c
Kelly

[GaryP]

As was mentioned earlier, if your carbon canister is spent, it will allow chlorine to leak past it and the chlorine will damage the membrane. I talked to one water treatment guy here in SA and he said he always installs an additional carbon canister as a back up to the first to help prevent this. An extra carbon filter is a lot cheaper then a new membrance every few months.

What happened in your case is that your membrane was allowing ions to pass through to the DI. The DI was quickly exhausted and the TDS shot back up. The DI resin is intended for polishing, not as a primary treatment stage.

[AlexKilpatrick]

Thanks for the tips. I will definitely try to replace the cardon filter more often. RO membranes are expensive!

I replace the membrane, and not the input is 250 and output is 400 (!) I'm assuming that is because of the preservative gunk in the membrane, and that it will go down after running a few hours of water through it.

[BuckeyeHydro]

Is everything up and running correctly now?

[AlexKilpatrick]

Yeah, it was a combination of a number of problems. It turned out I had the RO hooked up backwards :o I don't know how that happened. Having it backwards seemed to kill the membrane I had, so I replaces that with a 100 GPD membrane I got from a MAAST sponsor, added in the default flow restrictor they gave me, and now everything is working great.

[JimD]

Sometimes the obvious is impossible to see.

[AlexKilpatrick]

Sometimes the obvious is impossible to see.

Actually, it wasn't obvious to me. I looked at many times and assumed it was correct. It was just my understanding of how RO membranes work was flawed. I didn't realize this until I looked at another unit.

An RO membrane has 2 connections (call them A & B) on one side and one (call it C) on the other end.

A--|----------------|
B--|----------------|--C

I had assumed A was input, B was waste, and C was the output. My reasoning was the A was under high pressure, and the flow restrictor on B caused some of the water to be forced through the membrane to C.

However, I now know that A is input, C is waste and B is output, which makes no sense to me. I don't understand how the membrane works. Does the water flow through the center pipe of the membrane, and then back through the membrane to B?

However, in any case I was able to do a nice big 50 gallon water change with pure water and my tank already looks a lot better. Lots of things have perked up.

[BuckeyeHydro]

I think there is still confusion. Look carefully at the housing. One end has a single port. That is the "in" port.

Look at the other end of the housing. It has two ports. One is near the center of the end, and one is near the edge of the end. Purified water exits the housing from the port near the center of the end. Waste water exits the housing from the port near the edge of the housing.

[betiuminside]

I am about the recieve my system, can you guys put pictures??? so I don't screw up mine??? LOL..

[OldSalty]

Buckeye is so correct. the single port is ALWAYS the input. So in his display above C=INPUT, B=PRODUCT OUTPUT, A= WASTE WATER . SO Alex, ya till got it wrong, Give me a call tomorrow and I'll help ya with it. Betiuminside, PM me and I can come by and help ya with yours, we live really close. PM me with your details. That goes for anyone else in SA that needs help with their new or old units. Just PM me, I'd love to help ya all out if ya want it.

Kelly

Kelly

[betiuminside]

I will defenely will give you a call... it is supposed to be here tomorow. Thanks.

[AlexKilpatrick]

You guys are right (of course), I was posting it from memory. My system is hooked up right, and has been working well for about 100 gallons so far.

I still don't understand the path of water through the membrane, though. Does it flow throug the membrane from the inside to the outside? Or is it something else?

[BuckeyeHydro]

Water enters the membrane end near the brine seal and moves toward the center of the membrane - which is a hollow plastic tube with holes in it. Once in the tube it goes to the far end of the tube (away from the inlet port) where it exits the membrane and RO housing. That's why the permeate port (purified water) on the RO housing is the port in the center of the end of the RO housing.