Increasing TDS with airation and heater

[Bent17]

Out of curiosity - Does airation of TDS zero and having a heater heating up the water increase TDS?

 

[Fish Styx]

Good morning. Yes, polonged aeration can have an impact on TDS readings of liquid, in that evaporation of the liquid caused by aeration (decrease in solvent volume) can lead to an increase in the concentration of the solutes in suspension (TDS). Additionally, while TDS is directly correlated with conductivity, there exists a positive relationship between heat and TDS. As temperature rises, so too does ion mobility. Therefore, for every increase in temperature of 1 degree centigrade, one can expect an increase in TDS readings / conductivity of roughly 3%.

Now, what does this mean for us as reefers and hobbyists? The short answer is: not a lot really, especially when starting with 0 TDS RO/DI water. Now, could prolonged aeration of RO/DI draw dust and other particles from ambient room air into our water? Perhaps. In sufficient quantity to make an impact? I suppose that depends on what is in your room air. Having scented candles, incense, cleaning products, and the like in close proximity to your mixing station is probably not a good idea and should naturally be avoided. In the long run, however, the impacts of heat and aeration on our RO/DI as hobbyists are negligible, and not terribly concerning.

Hopefully you find this information helpful. Happy reefing!

Namaste.

 

[Bent17]

Thanks for that detailed explanation!

My Scenario:

I have a 100L tank which my RO fills up for WC. Now temp is very cold so inside this tank I have a pump for circulation and a heater to bring up the temp. Will test the TDS this evening before I mix my salt and check the TDS. The water this morning was TDS 0

 

[Fish Styx]

Thanks for that detailed explanation!

My Scenario:

I have a 100L tank which my RO fills up for WC. Now temp is very cold so inside this tank I have a pump for circulation and a heater to bring up the temp. Will test the TDS this evening before I mix my salt and check the TDS. The water this morning was TDS 0

I'd venture to guess that you're good. Especially considering that you're starting with a reading of 0 TDS and likely have a cap or cover on your storage tank / mixing station. Like I said, for our purposes as hobbyists, any impact these factors would have on our "finished product" would generally be negligible.

 

[Randy Holmes-Farley Verified Community Expert]

I'll just expand a bit on Fish Styx answer. Zero ppm TDs water should not get significant TDS just from heating, IMO. Most TDS meters correct for temp issues, except cheap inline meters, and a 3% increase of zero is still zero anyway

Aeration will increase the ppm TDS to about 1-2 ppm from CO2 from the air.

Larger increases than that will be coming from contamination of various sorts (salty dust, slow dissolution of residual material in the container, etc.)).

 

[Liftoff]

I'll just expand a bit on Fish Styx answer. Zero ppm TDs water should not get significant TDS just from heating, IMO. Most TDS meters correct for temp issues, except cheap inline meters, and a 3% increase of zero is still zero anyway

Aeration will increase the ppm TDS to about 1-2 ppm from CO2 from the air.

Larger increases than that will be coming from contamination of various sorts (salty dust, slow dissolution of residual material in the container, etc.)).

I bought a 40 L (10.5 g) BPA free/food grade canister and filled it with RO water of conductivity ~10 microS/cm for my ATO.
After 2 weeks the water in the canister read ~250 microS/cm (lid partially open to air; i also use this pump to make water changes, there is a possibility that there were some residual saltwater backflowing from the pump; i use the Tunze Osmolator nano; but i made a cleaning cycle before so i think an influencethere is unlikely).
I was thinking it is the ATO pump or similar but I made a test where I put several smaller buckets at RT with open lid. I observe again a slight increase in TDS (within a day from 14 uS/cm to 20 uS/cm roughly).
The TDS meter seems to be stable with a DI reference and the "freshly" made RO water at the 10uS/cm.

Is this a known effect in this context?
The temperature also rose today by a few degrees centigrade (maybe from 22C to 25C).
The room is clean, but can this be high CO2? Or just temperature fluctuations causing such an increase in TDS?
Many thanks for any help in this context.

Best
Liftoff

 

[Randy Holmes-Farley Verified Community Expert]

As noted an above, CO2 will add 1-2 ppm TDS, which corresponds to a few uS/cm.

250 us/cm is either from ions in droplets or dust getting to it, or something dissolving from off the surface, or possibly the very near surface of the plastic.

 

[Fish Styx]

As noted an above, CO2 will add 1-2 ppm TDS, which corresponds to a few uS/cm.

250 us/cm is either from ions in droplets or dust getting to it, or something dissolving from off the surface, or possibly the very near surface of the plastic.

Agreed! Contamination is likely the culprit here.

 

[Liftoff]

Thank you for the kind and fast response!

One last note, is the 3% increase per centigrade reliable?
Since the RO comes out at probably 16C, room is at 26C, would be 30%.
That's the 14 to 20 I have observed right there(?).
If that could be at least the explanation for the test i made today, does this affect the water quality negativley?

Best
Liftoff

 

[Fish Styx]

Thank you for the kind and fast response!

One last note, is the 3% increase per centigrade reliable?
Since the RO comes out at probably 16C, room is at 26C, would be 30%.
That's the 14 to 20 I have observed right there(?).
If that could be at least the explanation for the test i made today, does this affect the water quality negativley?

Best
Liftoff

Sorry for the delay, I was out to dinner with The Dainty Dictator. It is likely a combination of factors, but As mentioned, I agree with Randy here that it is most likely contamination. Really hard to tell unless you had precise volume measurements to correlate with your pre and post readings. Repeat the process and keep the lids closed this time to see if it happens again. It is also always best to ensure 0 TDS to begin with, not only for the health of your system, but to definitively determine that any increase can be attributed solely to contamination.

Swings in non-compensated readings won't impact you negatively.