RO/DI TDS readings.....too high?

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Aquarium Advice Freak
Mar 21, 2005
Well, I've never really had access to a TDS meter until recently....I always just changed all my filters about every 4 months to be safe.

My tap water reads 360ppm.....ouch.
I just changed all my RO filters and my DI filter too, and the TDS is 15ppm. Is this really that bad?

I was thinking I could add another DI stage at the end....I've read others doing this with success.

Any other thoughts?

If it fluctuates between 15 and 20 ppm, is this really a problem?

it all depends what the total dissolved solid is.. Is it good or bad?? no way to know without paying for a water test. I run my DI resin a long time, I usually let it get to 15-20 before I change it out. I also test for phosphates and nitrates to see if there getting by.
I run a 2nd Di unit and it has worked well for me. I rotate the second unit to the first spot and then add a new one to the last spot when they need changing.
Thanks seaham, that's what I'm thinking about too. It does test 0 for trates and p04, though.
My tap start out at around 215. RO is down to 5-7 and DI is 0. When it gets to 2-3 I change the DI cartridge out. 15ppm is not terrible. It's just a matter of what your comfortable with. Testing for PO4 and NO3 is a good idea.
Do you think adding a second DI on the end will take it down further (possibly 0?)
IMO yes.. 15 is not a big drop and the resin can take that out. Test your water before the DI and see what that number is. It is possible you membrane is not working at 100% how old is the unit.
The unit is about 9 or 10 months old......I think before the DI it runs about 25 or 30 TDS
If your resin is 9-10 months old then its time to change out the resin. My resin used to burn out in 2-3 months. Adding a second is not needed if your getting 9 months out of your resin, IMO that is great to have it last that long. The other filters should be changed out around 12 months and the Membrane they say can last 3-4 years.
sorry I missed that before..
sorry I didn't explain myself better.....all filters are brand new, just changed them--including the DI resin! It's a dual bed resin and it's the "add-on" DI that I bought. I think Jaiden may be on to something, because the DI does last a long time. I change all filters (except the membrane of course) every 4 to 6 months to be safe because I didn't have a TDS meter handy before.
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