View Full Version : RODI TDS Question

10/17/2011, 03:40 PM
I am getting 0 TDS from my RODI but I am getting mad algae still. Is it possible to still have contaminants in the RODI like a false reading?

10/17/2011, 03:43 PM
it could be false reading can u have some one else test it

10/17/2011, 03:44 PM
Yeah I can probably bring some to my local shop and see what they say.

10/17/2011, 03:52 PM
Remember that number has to have units. It's not 0 TDS. It's 0 ppm TDS. Parts-per-million is an important part of that reading (unless you have a really really expensive TDS meter). So say your RO water has 300ppb phosphate. The meter can say 0ppm or 1ppm. But it can't say anything in between. How should it read for 0.3ppm? Probably it will read 0.

Just like if you had a digital thermometer that only read to one degree precision, no decimal places. If the temp was 54.7, it would read 55. If it was 54.3, it would read 54.

If the temperature was 0.7 degrees, it would read 1. If the temperature was 0.3 degrees, it would read 0.

In analysis, zero never really means zero. Zero means undetectable at best.

10/17/2011, 03:56 PM
I hear ya so in other words i can actually have some degree of contaminants even though it reads 0 tds. Thank you for the input

10/17/2011, 08:03 PM
I hear ya so in other words i can actually have some degree of contaminants even though it reads 0 tds. Thank you for the input

Yup! At work we have on-line instrumentation that can measure boron down to 15 parts per trillion and Total Organic Carbon down to 50 parts per trillion in ultrapure water. Those levels are important for semiconductor and nanotechnology research. Way below anything that would upset the biology in a reef tank.

Look at it this way: if need be, we can make the water insanely pure. All it takes is money. :-) But how pure does it need to be? For reef tanks, the <1 ppm TDS is a pretty good yardstick.

Have you calibrated your meter lately? ;-)

10/18/2011, 07:59 AM
What do you put your "good" water in? Have you measured the "good" water after it's been in your container?

10/18/2011, 08:51 AM
I keep the water in jugs..my usual routine is I allow the RODI system to run for a bit maybe like 15mins or so then with a clean cup I test it to make sure I am getting 0 tds then I fill the jug and usual test about half way full of the 5 gallon jug to make sure nothing is wrong. My assumption is that my tds meter is off. I am gonna bring some water to my LFS and have them test it to see if its the RODI that is causing my algae outbreak. Thank you all for your help