The substrate idea was just a guess. I can’t verify that actually. You are right that for that to be happening maybe there’s undissolved salts sitting there. Seems unlikely though.
Thanks for all the replies. Much to learn!
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What else could it be? Remember the TDS is really an EC value which directly correlates to the # of free ions in solution. An almost immediate jump from 200 to 900 is hard to explain any other way.
Did make a misstatement earlier, indicated that an amino acid had the same effect per ion as an inorganic acid, similar value but not the same, pKa, temperature, and molecular size all play and each ion has a different EC vs concentration curve, and a different EC vs temp curve.
Hi Don. Don’t get me wrong. I don’t know these chemistry stuff too well myself. I just meant that substrates in the tank so how could it be undissolved if it’s already underwater. From a lay man point of view. You could very well Be right! Btw the tds example of 200 to 900 is actually someone else’s situation.
Cheers!
Frankly, I am kinda guessing here but in a non-turbulent setting (as in the water below the top of substrate) you will get a gradient where there is a somewhat higher concentration of heavier substances, with subsequent precipitation of less soluble salts even underwater (that's why some older aquariums show lime stains below the water line). Stir it up and they return to solution. If that's not what's happening, I am at a complete loss as to what would kick up the TDS. Frankly, I am no chemist, just recalling what I learned as part of pre-med requirements. I get that your numbers are not the same as Peewee's, his are a puzzle. What are your #s pre and post substrate cleaning?
Anyone else have an idea what would cause such a big change in TDS over a short time frame?
A TDS of 900 surely cannot be right ???
A TDS of 900 surely cannot be right @Peewee ???
I get readings of 950 several times. Beginning at around 250 for several weeks it shoots up to over 900 TDS in one day. As I continue to make daily water changes each day the TDS will drop by 50 or more. Such as 950 then mid 800s then 600s until eventually back to the high 100s to low 200s where it will remain for a time. Then suddenly back to over 900. The water is clear and the fish do not notice it. Like I said the continue to go about their business of eating, chasing around, and preparing for spawning.
If I were getting these readings I would get a second TDS meter, fairly cheap. If both read the same I would be at a complete loss.
You know this is so bizarre, I would start checking my source of water prior to adding to tank. Google Hanna Primo TDS tester.
Ignoring the rare times I get the results from stirring the substrate. I only get huge jumps if I dump salt or dechlorinator.
I agree, i think the salt could be it. Sea water has about 50X electrical conductivity and therefore TDS of average tap water.
You can skip getting a second TDS meter.