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Simple substrate test.

Aqua sobriquet

Aqua sobriquet

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Joined
17 Mar 2012
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Dorset
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! :lol:

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

IMGP1471.jpg


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

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
 
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,
 
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?
 
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?
Click to expand...
Please, don't know If that makes a difference, but I did wash mine, and not seen constant rises in tds.
 
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
 
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.
 
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
 
Just wait a minute... Thought the subject was "Simple substrate test".

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

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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