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TDS confusion.


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So being mindful about the possible issues that high tds levels can cause I have got a (cheap) meter and been keeping an eye on things.  Rainwater in my butts is not good.. probs because it comes off an asbestos garage roof and there will be significant debri build up in the butts too.  I have however collected rainwater direct into buckets that is very low tds. I have also got a good supply (from my friendly window cleaner) of ro water that is absolute zero.  Now using the zero stuff, or fresh rain the issue I have is that once the plants have been in trays for a while the tds increases. I use garland trays and capillary matting as recommended and supplied by recognised uk CP plant supplier.   After a fairly short period of time though the tds increases and significantly.  After 2 weeks one tray has gone from absolute zero to 235.  I will try and do a test with just the tray / matting and water and see what happens with time but is it the actual plants in the pots with soil that is causing this perhaps?   Confused. 
 

Any advice on this appreciated. Thank you. 

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After 6 months my (29€) AMTRA TDS readings started to alarm me.

WHAT'S HAPPENING TO MY PLANTS ??

I had at this time under strict control,  a bog with underlaying LECA balls well rinsed and cured for one months.
but you never know... better be safe then sorry..

After one month, suddenly I started to get reading over 200PPM , I quickly flushed it, believe me .. I was fast "!!!
 

Just to be there again after a few days.
Then, not only on that pot but also randomly from other as well ..
Well,  I started to doubt my eyes.

Then I decided to believe them, called Amazon... sent it back and got reimbursed.
Bought a similare model 3 time cheaper (9,30€) and with the difference bought some foliar fert.

It's 4 months I dont have anymore strange readings!!! 


( and yes, the bog never has to be flushed again.)

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On 11/8/2022 at 11:06 PM, AlainCh2 said:

After 6 months my (29€) AMTRA TDS readings started to alarm me.

WHAT'S HAPPENING TO MY PLANTS ??

I had at this time under strict control,  a bog with underlaying LECA balls well rinsed and cured for one months.
but you never know... better be safe then sorry..

After one month, suddenly I started to get reading over 200PPM , I quickly flushed it, believe me .. I was fast "!!!
 

Just to be there again after a few days.
Then, not only on that pot but also randomly from other as well ..
Well,  I started to doubt my eyes.

Then I decided to believe them, called Amazon... sent it back and got reimbursed.
Bought a similare model 3 time cheaper (9,30€) and with the difference bought some foliar fert.

It's 4 months I dont have anymore strange readings!!! 


( and yes, the bog never has to be flushed again.)

Can I get this right?  You are blaming it on a faulty TDS meter?  I actually have 2. will have a play and do some more testing to see what is causing this.  Thank you. 

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Water evaporation lead to a continuous increase in salts concentration in the tray/soil, just flush everything with deionized water when/if the salinity is too high for you. All the ions that went into the soil since you started using your trays are still there.

 

Clays are efficient ion exchangers, placing then in clean water for a while won't solve the salt leakage issue.

Edited by .Pico.
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5 minutes ago, .Pico. said:

Water evaporation lead to a continuous increase in salts concentration in the tray/soil, just flush everything with deionized water when/if the salinity is too high for you. All the ions that went into the soil since you started using your trays are still there.

 

Clays are efficient ion exchangers, placing then in clean water for a while won't solve the salt leakage issue.

Hi.  I don’ t use clay..   would evaporation lead to an increase in salts IF I only use absolute zero ro water to start with? 

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Hmm. TDS is not salts. If salt concentrations was high the plants would be dead. TDS is everything dissolved in the warer, good just as well as bad.

Just make sure that the water you add is good. Water in the tray will increase by time and are no problems If the start water is good. Stop looking at figures on a cheap measuring device and start look at your plants. If they look good there are no issues. That method is more reliable, more joyful and cheaper.

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6 minutes ago, Tropfrog said:

Hmm. TDS is not salts. If salt concentrations was high the plants would be dead. TDS is everything dissolved in the warer, good just as well as bad.

Just make sure that the water you add is good. Water in the tray will increase by time and are no problems If the start water is good. Stop looking at figures on a cheap measuring device and start look at your plants. If they look good there are no issues. That method is more reliable, more joyful and cheaper.

That is the point I was trying to make. There are no salts to start with unless the suppliers have used salt laden compost which I find extremely unlikely for obvious reasons. 

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I was talking about clays not to you but to the other person who answered.

The conductivity of water depends on ion concentration. These ions are produced by dissolution of salts or dissociation of dissolved neutral species, acids for example (the cation in the case of an acid is simply solvated H+). Every soil contains species that liberates ions when water is added. Be aware that "salt" does not mean only inorganic ones.

The deionized water you are using (rainwater, produced by reverse osmosis, etc...) is not ion free at all, simply their concentration is much lower than that of your tap water.
To obtain pure water (which is needed for example for chemical analysis or other critical applications) you need (very expensive) multistep procedures which involve a combination of different strategies. But this would be absolutely pointless for horticultural uses.

Your tester is saying " 0 " simply because the conductivity of your solution is too low for the resolution of your instrument, which is therefore measuring 0.

To be more specific what you are measuring with those testers is water conductivity. This conductivity value that you are measuring, and which is usually expressed in uS/cm (EC tester does exactly this), is then converted by these TDS testers to a different (pointless) artificial scale (in ppm) which compares the conductivity measured with that of a KCl solution of a defined concentration. This is done simply because things addressed to the consumer market needs to always "look simpler to understand", and apparently something expressed in parts per million  "of potassium chloride that you would need to prepare another solution of comparable conductivity" seems more understandable than a value of tnhe actual measurement in micro Siemens / centimeter. The result is just confusion.
Then, of course, they even managed to mess this up by creating different scales in different countries and expressing all of them in "ppm" without even differentiation...

 

TDS is absolutely not "everything that is in the water", be very careful about this. You can also easily see this in practice by dissolving non ionizable compounds in water and testing the resulting solution. You can use sucrose (sugar) for example.

Edited by .Pico.
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Excuse my sloppy approach. I don't have any chemistry education and I am not practiceing tds measuring. I have been in the aquarium hobby and plant growing hobby for 40 years with some level of success without ever measuring TDS. I did measure micro Siemens for a while, but found it pointless. Wheather it is animals or plants, understanding their native environment and observe the progress has allways been a success way for me. If one read somewhat high tds and the plants are fine....Well, the plants are fine so don't worry. If you measure high tds and your plants is not fine, the human mind would instantly draw the conclusion that tds is the reason. While in fact it is not certain and you may waste energy and time on correcting something that don't need correction. 

Tds is by definition dissolved ions, including salts, minerals and metals. Not all minerals are salts. No metal is a salt. Not every mineral and metals are instantly bad for your plants (to my non educated brain)

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Well, actually pretty much all of what you listed, if we don't include eventual suspended solids, is a salt, if it's dissolved in water. Every solubilized metal is in saline form.

Of course there is no "good" or "bad" stuff. No organisms would be able to grow in pure water. But a lot of carnivorous species do not tolerate high salinity.

Here no one ever suggested him that he must have readings close to 0 in his trays, but he stated that water collected from his roof has high salinity, and I guess he could have used it for his plants in the past.

"235" ppm is more than 350 uS/cm which is pretty high and I wouldn't be confortable with such readings in my trays, except eventually immediately after some particular treatments. I'm pretty skeptical you can reach such values by just soil decomposition. Considering that flushing the soil once in a while is always a good thing in any case, I would do it right now before eventual damages on the plants starts appearing.

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Oh dear..I have started something.  Which is good for discussion but,  I never said the water collected from my roof had high salinity, just higher in ppm of tds.    I am an amateur with CPS. Ut have experience with cacti etc.  I disagree with you saying that plants cannot grow in pure water, especially Cps as they can get their nourishment from elsewhere and that is what they are and why they do it.  

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Hmm, to my basic knowledge metals dissolved in water is in its ion form, not as salt. For exemple ferric cloride is a salt. If dissolved in water it will exist in the water as ions of Iron perchloride and hydrocloric acid. Iron perchcloride is not a salt as far as I understand. I am not here to make an argument for the sake of arguing. I think that I as well have something to learn from such discussion.

Edited by Tropfrog
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  • 3 weeks later...

Just use your collected rainwater and don't worry - too much use of the TDS meter will only confuse... Run off from most non-cement based roofs will be fine even if a bit higher TDS than you expect. Measuring the standing water in your trays is almost pointless and is not generally related to water hardness (which is what matters). PM if you want more details, posting results in a fair bit of poorly informed responses. I'm not a water chemist, but am a chemist who's dealt with ultrapure water in the past.

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