Correlation between TDS and SW

Being mostly new to all of this, curiosity runs rampant so I wind up doing strange things that would leave most saying "*** was he thinking?"

So I test a new "batch" of RO/DI to make sure I'm still at 0 -- perfect.
I mix the salt in my WC tank and let it aerate/mix.
I check TDS of saltwater for curiosity sake and it's much higher than I had anticipated..why I anticipated anything is anyone's guess.

That got the gears churning in my brain. If you could keep as many variables under control as possible to avoid mixed results, is there a potential to guesstimate salinity of your SW from your TDS results?

I realize you must have precise control of the amount of salt you need and, more than likely, different brands of salts or even different batches of the same brand could result in different TDS readings since there is more than JUST salt in varying ratios.

Obviously, a TDS meter would never be able to replace a refractometer or even a hydrometer but the whole idea made me think a little.

Anyone care to shed some light on this?

 

Interesting. If the water you are mixing salt with is truely zero tds water, idk why this wouldn't work. A hydrometer doesn't really measure "salinity", it measures specific gravity. It seems like the tds meter would be doing the same thing.

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Makes complete sense. It should be nowhere near zero in saltwater. Think of all of the Calcium, Magnesium, Iron, alkalinity the salt mix added (in addition to the minor elements).

Moral of the story, TDS meters will tell you nothing in saltwater. It's for freshwater ony.

 

No, you could have two different mixes at the same salinity and get two different TDS readings. Some mixes might have more sodium Chloride ions but less major elements. Basically, it's a useless measurement.

 

Correct. I'm going to set up a control and a spectrum of mixtures with my ro/di water to see what comes up when my refractometer arrives tomorrow. That way I'll be able to to test different mixture ratios. Again, this is all in the name of curiosity and a TDS meter would never be a fair replacement for proper specific gravity testing.

Edit--one would have to make a (poor) assumption that the bag is properly mixed and you would be getting negligible differences in elements per part.

 

If I'm not mistaken, you can ruin a TDS meter by using it in saltwater. It's not it's intended purpose.

 

BTW, here is a good article, in case you haven't read it:
What is TDS? by Randy Holmes-Farley - Reefkeeping.com

 

This was the answer I was looking for! Great read, btw.

 

You cannot measure the TDS of saltwater with a TDS meter, its going to be over 32,000 ppm measured as TDS and the common TDS meter only reads to 999 TDS. Some will read to 9999 by tens but have little accuracy and its still much lower than new saltwater.

Make darn sure you triple rinse your TDS meter in RO/DI or distilled water so you don't ruin the probes with the saltwaterand always rinse with RO/DI before putting it away with the cap on it.