I back flushed the membrane on my RODI unit for about a minute before I started making water yesterday. Usually, after the backflush I let the water run until the inline TDS meter reads 0 on the output, dump the accumulated water and start collecting. I never went back to dump the water and didn't think about it until I got back home to a full can. I have a handheld TDS meter that I decided to try out to see what the water would measure. I got 14 tds. I had a small amount of water from the previous batch done with my usual procedure and it read 8. I have two inline TDS meters on my 7 stage RODI. Usually the TDS on the input reads 1-2, the output ticks up briefly then drops to 0. I read my tap water and I got 50 on the handheld, the highest I have ever seen on the RODI inline unit is 6. I'm not sure which meter to believe. I have read that for the handhelds anything 10 or less is essentially 0. Should I be concerned? My filter media is due for a change in November, but my mixed bed resin is still blue. I read my tap water and I got 50 on the handheld, the highest I have ever seen on the RODI inline unit is 6. I'd be less concerned if it weren't for the GHA battle I've been having in my display.
Hand held TDS meter vs inline TDS on RODI
- Thread starter Cook
- Start date
Depending on the container storing the RODI water, you might get a slightly higher than 0 reading for TDS with a handheld. Some handhelds are more reliable than others. You also might want to test your handheld meter at your LFS or a fellow reefers so you can see the range of that unit compared to others. And of course you should flush your system before making water after changing cartridges or media and measure to make sure you are good. An in-line monitor for TDS works best for measuring to know when it is all good. If your tap is actually that high, then you might want to get the house water tested so you can see what is in it and what the best filters would be for your RODI unit if your water company does not publish that info. For areas that have different problem water supplies, you can usually figure out the best filter set ups to take care of your issues. Sometimes if a filter is damaged or breaks, then the TDS will be elevated. If all other measurements in your tank are good- proper nitrate phosphate levels and ratios, good salinity, calcium and magnesium and no contaminants, and you have algae outbreak that is not usual for your tank- elevated TDS can cause this. Check all your cartridges to see if any are broken. Think about adding to your setup or cartridges used if you are not getting 0 TDS output.
I measured some distilled water with the handheld TDS meter and it measured 3 before I rinsed the container and 0 after. I have a calibration sachet I can check the meter with. I ordered all new filters and a spare membrane to have them on hand.
Well that makes two of us. However, it's not a sure thing yet. I stopped by an lfs and picked up 5 gallons of RODI. I took it home and measured their water and it was 37. The water in my RODI can measured 0 today when it measured 14 Monday night. My tap measured 48, which is pretty consistent to the 50 I got Tuesday night. Also, of course BRS now has the 7 stage kits back in stock after I ordered everything individually and took a lower grade of mixed media since that is what they were out of.
I've been doing some more testing and my latest batch of water measured 0 earlier this week with the handheld, which matches up with my inline RODI meters. So, I don't think this was a contributor to my GHA issues. I added the three stages 18 months after setting up my original BRS 4 stage, so the inline TDS meters were 18 months apart in age and I think it unlikely they would both go bad. Tap water still measures higher, 47 this time. I poured out the LFS purchased RODI as it measured 36 a week later, I'll stop by this week an ask them to take a look at what they are making once I have confirmed my handheld is calibrated with the TDS solution I got. What I considered good stored RODI originally was in a squeeze bottle that I use for rinsing my test kit cuvette's so it's possible that had a higher value, I don't know what kind of plastic it is. One thing I like is that the TDS really isn't increasing with my stored RODI in my trash can, not a big deal since I usually only make a week's worth at a time, but nice to know.
