TDS meter and its readings advice

[ksicard]

I decided to buy a TDS meter about two weeks ago to see if I needed to replace my filters since it had been a long time since I had done so. I checked my TDS and as suspected it was much to high for my likings at 65ppm, so I replaced all my cartridges and membrane on my 4 stage RODI unit. After changing all the cartridges I checked my new water and it had a TDS of 2ppm. I was very happy with the results, but what's strange is I've tested each new batch of water since then and the TDS has continued to climb up. My fresh water is now reading 45ppm and I dont understand it. Could anyone shed some light on this? It's only been two weeks since I got the 2ppm reading. It's a HM digital TDS meter that I got from the LFS.

 

[saltfan]

Thats way high TDS should read 0. Did you change the DI resin thats the final step. Any time I start to read any TDS I change the DI resiin and it goes back to 0.

 

[ksicard]

I literally just changes all filters and membrane two weeks ago, that includes the DI filter. The TDS doesn't seem to affect my tank, nitrates at 2ppm and phosphates at 0.04ppm. Something isn't right, I'm thinking it's the TDS meter but I'm not sure.

 

[DaveK]

If your in doubt about your TDS meter, you can buy a bottle of distilled water and test that. That will give you a known good standard to validate your TDS meter with.

While it's possible for this problem to be your TDS meter, more likely this is a problem with your RO/DI unit. In that case, you will need to back track through the unit, and see where the major issue is. I suspect you have a problem with the RO membrane itself, and that it is either damaged or not correctly installed. You may also have to replace your DI cartridge. It may have been doing all the work and now is used up.

 

[ksicard]

DaveK how can the membrane be improperly installed? don't you just slide it into the membrane tube on the RODI unit? I'll take it all apart and make sure it's all fitting correctly.

 

[DaveK]

If there is any way for water to bypass the membrane, it's not properly installed. Remember these are run under fairly high water pressure. I had one once where it wasn't quite properly seated, and water was getting by. Externally it was not leaking, bit the TDS reading was high. Also the membrane can get damaged. If it gets a hole in it, it's bad and needs to be replaced.

Typically out of the RO unit you should be getting a TDS reading of about 4 to 8 pp. If it's a little higher, that could be OK, but why your getting 45, something is way wrong.

 

[ksicard]

You were absolutely correct DaveK, I re seared all my filters and membrane and that seemed to do the trick. Getting 2ppm on the TDS meter, also the meter says on instructions that often when the TDS is 0 the meter reads 2ppm so I'm happy with the final results. Thanks again.