# Simple substrate test.



## Aqua sobriquet

I read somewhere that some substrates increase TDS whilst other quite similar looking stuff actually reduces  it. Although there are probably very good reasons for this it didn't seem particularly logical to me. Why for example, would two fired clay products react so differently? 

Well I don't know why, but as I have a few different substrates to hand perhaps I could take some simple readings with my new TDS Meter just to satisfy my own curiosity! Nothing too scientific but it's not costing me anything except a few moments of my time. 

This is what I've done. I have to hand three fairly similar looking substrates: JBL Manado, Tesco (moler clay) Cat Litter and Colombo Flora Base (small pellet)
I measured 50ml of each material and placed it into a beaker (unwashed) and topped it up with water. I used supermarket spring water with a starting TDS of 106. Not sure why but that's what I used! As a point of interest I weighed each dry 50ml sample with the following results: JBL Manado 40g, Tesco C/L 28g and Flora base 46g.
Others have noted that some substrates are attracted to a magnet so I put a small magnet into each dry sample in turn and found they all demonstrated this phenomenon. After gently adding the water I noted that the Manado sample went a little cloudy, the Tesco C/L went very cloudy and the Flora base stayed quite clear. 24 hours later and the Tesco sample still does not look completely clear but the other two look good, particularYly the Flora Base. 

These are the start TDS readings of the samples:

Manado 131
Tesco 174
Flora Base 106

After 4 hours I took another reading:

138
184
101

24 hours after first reading:

170
222
91
----------------
204
290
85
----------------
238
370
86
----------------
273
408
86
----------------
307
486
86
----------------
327
528
89
----------------
348
578
89
----------------
355
599
88
---------------
375
650
88
---------------
403
690
90
---------------
I'll take readings now every 24 hours until I get bored or the readings level off - whichever comes first!  

The samples, taken just after adding the water. For some reason they look clearer in the picture than they actually were:






Manado on the left, Tesco in the middle and Flora Base on the right.


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## sr20det

Did you wash the cat litter?

Awesome test by the way.  Been going crazy with mine.


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## Aqua sobriquet

No, all samples were unwashed. I did start to wash some but I was losing a lot of it through the sieve. If I can find a finer one maybe I can retest the Tesco.


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## Alastair

Isn't the columbo different thiugh as its not just purely baked clay it also contains nutrients and ph reducing properties etc??? 


Sent from my iPhone using Tapatalk


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## Aqua sobriquet

Not sure what it is, they call it aquatic soil. It certainly seems to be reducing the TDS somehow though! Pretty sure I'll be using it in the new Nano...


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## sr20det

Aqua sobriquet said:
			
		

> No, all samples were unwashed. I did start to wash some but I was losing a lot of it through the sieve. If I can find a finer one maybe I can retest the Tesco.


It's perfumed, so really needs a wash as not sure what effect that perfume has on the tds.  Washed a few times, will help, and same time causing less cloudiness.  Kill two with one.


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## Alastair

Aqua sobriquet said:
			
		

> Not sure what it is, they call it aquatic soil. It certainly seems to be reducing the TDS somehow though! Pretty sure I'll be using it in the new Nano...



Yes the columbo is the same as the Ada soils etc. I use it in my puddle at the moment. 


Sent from my iPhone using Tapatalk


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## ceg4048

Hi,
    The CEC and AEC of the clay are responsible for pulling ions from the water column. The impact of this ion exchange is to lower the TDS. All clays are not created equally and they will vary in the strength of their CEC/AEC. So the type of clay used is a factor.

On the other hand, as Alastair mentions, some products are enriched with NPK, trace elements as well as organic carbon residues which will all dissolve in the water column and which will therefore have the tendency to raise the TDS.

The total effect on TDS will be the result of the effect of these two factors. The balance of forces will change over time as the chemicals dissolve out into the water. A product that initially tended to raise the TDS will usually start reversing this trend after a few months. As the sediment matures with bacteria, and as organic waste settles in, then the Redox reactions occurring at the bacterial level will also have an impact on the overall effect. A better test therefore is to observe the effects of the sediments after a longer term. It's likely that these effects will more or less even out.

Cheers,


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## dw1305

Hi all,
Clive is right it is all to do with AEC and CEC of the clays, and yes some substrates can considerably reduce TDS initially. 

There is an explanation in the Akadama thread <http://www.ukaps.org/forum/viewtopic.php?f=17&t=741&p=175752&hilit=low+base+saturation#p175752>.

cheers Darrel


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## Aqua sobriquet

I'm getting a bit bored with this now but here's the latest reading ...   

443
785
101


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## Tim Harrison

Don't you dare give up, this is good stuff which cold help a lot of planted tank enthusiasts out...albeit eventually...


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## Aqua sobriquet

It's the "eventually" bit I'm not too keen on ...


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## sr20det

Aqua sobriquet said:
			
		

> I'm getting a bit bored with this now but here's the latest reading ...
> 
> 443
> 785
> 101



Dont get it, Tesco seems to be rising, whereas mine settled now for a month or two, seems to be on par with my tap water?  Not rising either?


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## Aqua sobriquet

Both the Tesco and the Manado have shown a steady increase. Only the Flora Base has shown any stability out of the three. But, as titled this is just a simple test taking TDS readings of the samples in beakers. I have some washed Tesco CL in a sack in the garage I could start to test in the same manner if folks want?


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## sr20det

Aqua sobriquet said:
			
		

> Both the Tesco and the Manado have shown a steady increase. Only the Flora Base has shown any stability out of the three. But, as titled this is just a simple test taking TDS readings of the samples in beakers. I have some washed Tesco CL in a sack in the garage I could start to test in the same manner if folks want?


Please, don't know If that makes a difference, but I did wash mine, and not seen constant rises in tds.


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## Aqua sobriquet

Ok, I've started a new one with washed Tesco CL. I'll take a reading once it's settled a little.

Todays readings:

Manado         440
Tesco CL       781
Flora Base     99
Washed TCL  183


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## sr20det

Aqua sobriquet said:
			
		

> Ok, I've started a new one with washed Tesco CL. I'll take a reading once it's settled a little.
> 
> Todays readings:
> 
> Manado         440
> Tesco CL       781
> Flora Base     99
> Washed TCL  183




Tesco CL       781,

wow, thats huge.


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## plantbrain

The test will illustrate the leaching effects over the short term(weeks).

It does not show nutrients etc or bioavailability/growth rate differences for plants.

There is a rather easy way to do that however.

Use the same amount of water and soil types in flask and place a soft but relatively air tight sponge at the flask neck and wrap around the stem gently.

Use something like an emergent aquatic plant, say Ludwigia repens.

Place in the window or a hot house etc. 

Measure the leaf no# and the stem length over time, take pics for visual differences.
Use 3-4 plant/soil flask per treatment.

So say you have 5 soil types:

You will need 25-30 flask and stems of the plant.
3-4 treatments then a control(say hoagland's solution(upper non limiting control) and then DI pure water(no nutrients, lower control). All other results should fall in between these 2 controls.

Measure the leaf and length weekly over say 8-12 weeks.

This is not hard.

CO2 will be non limiting as well as light.
So only the nutrients from the soil will be at play.

While not entirely natural like aquariums........it's a better test without other confounding factors.
This way you can conclude something growth wise about the sediments.


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## dw1305

Hi all,
The TDS reading is all to do with the exchange sites on the clays that form the substrates. They are exactly what they say they are "exchange" sites, ions will be exchanged along concentration gradients with the water. This is slightly complicated by the strength of the bond between each ion (the lyotropic series). 

Lyotropic series
Al3+ > Ca2+ = Mg2+ > K+ = NH4+ > Na+

I'll ignore the Anion Exchange Capacity (AEC) as:


1. it is typically about 1/10 of the Cation Exchange Capacity (CEC), 
2. is most significant in acid conditions 
3. and clays with a high CEC typically have a low AEC.
 This wouldn't necessarily be true of laterite etc. Details here <http://www.ukaps.org/forum/viewtopic.php?f=17&t=21739>

There are some CEC values for Moler clay (the un-perfumed base material for the cat litter) in this thread <http://www.ukaps.org/forum/viewtopic.php?f=17&t=11888&start=10> & <http://www.inex.fi/english/company/supplier/damolin.php>

The continual rise in conductivity from the cat litter is because cations (probably Na+ or K+) on the cat litter are being exchanged for H+ ions (protons) from the water. Protons are held about as strongly as potassium (K+) ions.

The cations are probably from perfume, although it is possible that the clay itself may be relatively mineral rich, as although the diatomite is almost 100% SiO2, it has seams of volcanic ash amongst the clay.

There are details for Damiolin diatomite here: <http://www.bgs.ac.uk/research/international/dfid-kar/WG92039_col.pdf>, I haven't read all of it, but it looks very interesting.

cheers Darrel


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## Nathaniel Whiteside

Just wait a minute... Thought the subject was "Simple substrate test".

I have an overwhelming urge to lay down now... 

I was fairly good in science at school but all this talk, well and truly blows my mind.

Every time Clive posts I get headache! Not saying its a bad thing, wish I had some of your twos knowledge. 

Im going to have to read into stuff more to understand what you mean!

Theres a quite a few members on this forum with a vast amount of subject knowledge, and I thank you all for sharing it with us.

Regards,


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## dw1305

Hi all,
It is reasonably straight forward. 

*Conductivity*
All the metallic cations (Ca++, Mg++, Al+++, K+) will conduct electricity. These ions (charged particles) are formed from the complete "disassociation" (it just means they dissolve completely) of any salt (they are called salts after "real" salt (NaCl), because they all make the water taste salty). 

Water is "covalent" and the OH- and H+ "ions", don't conduct electricity. As we add (dissolved) salts we add ions, which conduct electricity, *more ions = more conductivity* in a linear (straight line) relationship. 

*CEC*
Some compounds, like clay and humus, have negatively charged sites (-)  on their surfaces which can exchange cations with the water. You can think of it like velcro, the cations are held, but not permanently stuck. If a clay mineral has lots of Na+ ions on its surface it will exchange them for nearly all other cations, Ca++, Mg++, K+ etc in the water column. This won't have much effect on conductivity, if the exchanges cations are all metals, but if the exchanged cations are non-metallic _e.g._ NH4+ or H+ ions, conductivity will rise as the Na+ ions will conduct electricity, whereas the H+ ion doesn't and the ammonium ion (NH4+) only conducts weakly.

*Substrate*
Akadama, for example, has a low _"base saturation percentage"_, this just means that it comes from a wet climate, where over time the rain-water has washed all of the other cations from the exchange surfaces, just leaving the tightly bound aluminium (Al+++) and iron ions (Fe+++), and the less tightly bound H+ ions.

If we put Akadama into *alkaline "water" with lots of calcium ions (like tap water from limestone aquifers we get in the SE of the UK), Ca++ ions in solution will be exchanged for H+ ions from the Akadama, the base saturation percentage of the Akadama will rise (more calcium ions bound) and the conductivity of the water will fall *(less calcium ions in solution, and replaced by hydrogen ions that don't conduct electricity).

*Cat litter*
In the case of the cat litter it initially has either: 
1. A very high base saturation percentage, which means H+ ions in the water (which don't conduct electricity) are being replaced by metallic cations (which conduct electricity), or
2. Dry compounds present that will dissolve and go into solution as ions, raising the conductivity
In either case *more ions = more conductivity*.

cheers Darrel


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## clonitza

Thanks Darrel for the clear explanation, I really don't think anyone may come with a better one. 
Do you know why some soils harm some shrimp species and others don't. I can see some clues in your post above but I don't want to guess. 

Cheers,
Mike


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## sr20det

so, by adding RO water in a water change, doesnt neccessarily lower TDS as the clay will release what it has collected? In layman terms?


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## Aqua sobriquet

Latest reading

448
785
95
260


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## dw1305

Hi all,


> by adding RO water in a water change, doesnt neccessarily lower TDS as the clay will release what it has collected?


 Quite possibly at first the TDS won't go down, but if you carry on adding RO, over time the exchange sites on the clays would become filled with H+ ions. This might take quite a long time to remove the more tightly bound multivalent ions (Ca++ etc) as they are higher up the lyotropic series than H+, and will only be exchanged when there is a very large concentration gradient between the clays exchange surface and the water. 

By the look of "Aqua sobriquet's" figures you would need to wash the "Tesco's Cat Litter" in quite a large volume of salts poor water, before use, if you wanted to maintain soft, low conductivity water in your tank. My suggestion would probably be to leave it out-side for 6 months with the rain washing through it, which is going to be impractical for most people, or to use it with plants and fish that don't mind harder, higher conductivity water. I like it as a substrate, and probably for most people it isn't going to matter that it initially may make your water harder.

I recorded the conductivity of the 3 tanks in the lab this morning, they all have water changes with rain-water and they have all been set up for at least a year.

The rain-water was 100 microS, _Dicrossus_ tank was 80 microS (100% silica sand substrate), the nano with Tesco Cat litter and a lid was 170 microS and the 3rd tank (another nano) open top and 100% silica sand substrate was 125 microS. 

cheers Darrel


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## gmartins

plantbrain said:
			
		

> The test will illustrate the leaching effects over the short term(weeks).
> 
> It does not show nutrients etc or bioavailability/growth rate differences for plants.
> 
> There is a rather easy way to do that however.
> 
> Use the same amount of water and soil types in flask and place a soft but relatively air tight sponge at the flask neck and wrap around the stem gently.
> 
> Use something like an emergent aquatic plant, say Ludwigia repens.
> 
> Place in the window or a hot house etc.
> 
> Measure the leaf no# and the stem length over time, take pics for visual differences.
> Use 3-4 plant/soil flask per treatment.
> 
> So say you have 5 soil types:
> 
> You will need 25-30 flask and stems of the plant.
> 3-4 treatments then a control(say hoagland's solution(upper non limiting control) and then DI pure water(no nutrients, lower control). All other results should fall in between these 2 controls.
> 
> Measure the leaf and length weekly over say 8-12 weeks.
> 
> This is not hard.
> 
> CO2 will be non limiting as well as light.
> So only the nutrients from the soil will be at play.
> 
> While not entirely natural like aquariums........it's a better test without other confounding factors.
> This way you can conclude something growth wise about the sediments.



I'd say that if the objective is to test for differecnes in substrates alone, there is no need for positive or negative controls. Growth being different (or not) among substrates suffices as a result,  all else  being equal. Just control variability in initial plant measures (e.g. length) and measure things before and after the experiment (and saving some flasks here).

I would also stress the need to label each flask and display them at the window sill at random (or haphazardly at least) so that replicate flask belonging to different treatments (substrates) are all interspersed. This will ensure position of the flask is not a confounding factor (e.g. substrate x was closer to the window and hence more light,...).

anyways, for most of us, I think this would be overkill for a home experiment...

GM


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## Aqua sobriquet

TEST OVER. Unfortunately I've not had the time to take readings or keep an eye on things and I've inadvertently let some of the contents evaporate so it's pointless to continue with the samples.   

The other half will be pleased to get the Kitchen table back ...


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## plantbrain

The kitchen table is now free


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