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Perplexed about extreme TDS readings

MichaelJ

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This is my first post here (Hi!).. and hope I am posting to the right thread.

My TDS in both my heavily planted 40g tanks are in the 1500 ppm range, and I do not understand why it is so high.

My general readings for both tanks:
KH 6-7
GH 8-9
Ph 6.8 - 7.0
Nitrate levels around 20 ppm.
Nitrite and ammonia ~ 0 (untraceable)
Phosphate 5-10 ppm
Not adding CO2.

Both tanks are about 8 months old.


I fertilize with Tropica Premier (14 ml - or 6 pumps) once a week after 20% WC and 5 ml Seachem Trace and 5ml Flourish Comprehensive mid week. Thats it. Most of my plants are doing really well. My 20% WC is mineralized RO water. The TDS is about 2-3 ppm when pure and about 280 ppm after mineralization using Seachem Adic buffer, Alkaline and Equilibrium.

I did think my TDS meter was at fault, but with a solution of 1 liter RO water and 0.5 gram of table salt the TDS comes out around 550 ppm. 1 gram of salt in 1 liter of RO water around 1200 ppm, so I am assuming the 1500 ppm readings in the tanks are probably a fairly good indicator that the TDS is on the extreme end.

Other than plants I only I have drift wood. The substrate in both tanks are CaribSea Eco-Complete (Red) planted tank substrate which should be inert. As plants and fish (tetras, Rams and angels) are doing great, I am really mostly curious rather than worried about it.

Cheers,
Michael
 

ceg4048

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Hello,
Assuming your probe reads accurately, the next suspect could be your acid buffer (which you really don't need). Acid buffers used to be made from highly toxic phosphoric acid, but the marketing on that product seem to imply that it is not H3PO4. It claims to convert Carbonate and/or bicarbonate to CO2 and the mot obvious agent would be Carbonic acid, a favorite of cola and other fizzy drink bottlers.
It could be that the acid is dissolving something in the tank i.e. something containing chalk or limestone so that the residue shows up as TDS. Try not using any of the buffers and just remineralize with Equilibrium.

The next suspect, of course, would be the plants themselves, which can dump large amounts of carbohydrates into the water, which again shows up as TDS. This usually happens in CO2 injected tanks and would be unusual in non-CO2 tanks like yours.

Cheers,
 

MichaelJ

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Thanks for the helpful insights.
So the Seachem Alkaline Buffer I use to (raise) target the 6-7 KH range (for Ph buffering). However, since that raises the Ph of the RO water from 7 to around 8.5, I am adding the Acid Buffer to bring the Ph back down to the neutral range. I am trying to make the RO water (with respect to Ph, KH and GH) close to identical to that of the tank water. Perhaps thats a misconception?
I am not a big fan of adding all those abrasive chemicals anyway, so if there is a way I can just raise the KH without raising the Ph then it should be fine I suppose. Otherwise, if I don’t add the Alkaline Buffer my KH would slowly wind down with each WC and eventually become too low (after about five 20% WC’s). Or, if I only add Alkaline and Equilibrium my Ph would drift upwards and eventually be too high for the fish.

I will try only Equilibrium for a couple of WC’s to see how how that works out.

Another thing I was wondering about is plant decay. In a heavily planted tank its sort of hard to get in-between the plants and clean up. I think I am doing an okay job, but there are always spots I cant get to without messing things up. Perhaps that a contributing factor to the extreme TDS as well.

Thanks!
Michael
 

jaypeecee

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The substrate in both tanks are CaribSea Eco-Complete (Red) planted tank substrate which should be inert.
Hi @MichaelJ

I am unable to determine if CaribSea Eco-Complete (Red) has the same composition as Caribsea Eco-Complete (Black). But, I suspect they are essentially the same - apart from colour. If that is indeed the case, then I think the answer to your question lies with this description:

"Contains Iron, Calcium, Magnesium, Potassium, Sulfer plus over 25 other elements to nourish your aquatic plants.

Eco-Complete Planted Aquarium Substrate contains all the mineral nutrients needed for luxuriant aquatic plant growth without nuisance algae!"

It's certainly not inert!

JPC
 

dw1305

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Hi all,
Welcome Michael,
I'm sorry that the links in this contains so much chemistry, but it all takes a bit of unravelling.
so if there is a way I can just raise the KH without raising the Ph then it should be fine I suppose.
Not really, pH in carbonate buffered water (water with some dKH) will always end up about pH8, because of the <"CO2~carbonate equilibrium">. If you add more dKH (an H+ acceptor) then you need more acid (a H+ donor) to convert that HCO3- to CO2.

The pH value is dependent upon <"the level of CO2 in the atmosphere"> (about 415 ppm CO2). It is the dKH ~ CO2 relationship that we use in a <"drop checker">
So the Seachem Alkaline Buffer I use to (raise) target the 6-7 KH range (for Ph buffering). However, since that raises the Ph of the RO water from 7 to around 8.5, I am adding the Acid Buffer to bring the Ph back down to the neutral range. I am trying to make the RO water (with respect to Ph, KH and GH) close to identical to that of the tank water. Perhaps thats a misconception?
Yes, it is a misconception, with the buffers you are <"giving with one hand and taking with the other">. The sellers of "pH buffers" are, at best, disingenuous about what their products do, and their <"advertising implies all sorts of things">, without ever making a statement that is provably false.
........ and about 280 ppm after mineralization using Seachem Adic buffer, Alkaline and Equilibrium.
I wouldn't add anything to raise dKH or dGH before you add your fertilisers. If you want to add a <"little bit dGH and dKH"> you can use a DIY mix, details are at <"James' Planted Tank">. If your tap water is hard? <"you can just add a bit of that">.

I don't actually worry too much about pH, because as you approach pure H2O (like your RO) pH becomes of <"very limited value">. This is because pH is both a ratio and a log10 value. I tend not to worry too much about pH in soft water, because it can never be stable and small changes in water chemistry cause large changes in pH.
My TDS in both my heavily planted 40g tanks are in the 1500 ppm range, and I do not understand why it is so high.
I did think my TDS meter was at fault, but with a solution of 1 liter RO water and 0.5 gram of table salt the TDS comes out around 550 ppm. 1 gram of salt in 1 liter of RO water around 1200 ppm, so I am assuming the 1500 ppm readings in the tanks are probably a fairly good indicator that the TDS is on the extreme end.
Looks like that is a genuine value (but as <"electrical conductivity microS, rather than ppm TDS)">, you've checked against a standard, if any-one is interested the <"working are here">.

My simple answer would be just add less fertilisers until the number comes down. I use a <"conductivity datum range"> and plant health, rather than adding nutrients regularly.

cheers Darrel
 

Wookii

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This is a strange one - something is definitely off with the numbers somewhere.

As Clive says you don’t need to add the Acid buffer. All it’s doing to removing the carbonates you are adding with the Alkaline buffer. Just add enough alkaline buffer to target 1-2dKH, and the Equilibrium for GH, and don’t use the acid buffer.

It could be that the acids you are adding in the buffer are reacting with the Eco Complete - though I would have thought there’d be more reports of high TDS in CO2 injected tanks with this substrate if that were the case.

Either way 1500ppm is extremely high if you are using RO (and even if you weren’t).

The only other thing I can think is something is throwing off your TDS meter. Have you tried taking the TDS measurement in a glass of tank water, rather than directly in tank?
 

Wookii

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My simple answer would be just add less fertilisers until the number comes down. I use a <"conductivity datum range"> and plant health, rather than adding nutrients regularly.

cheers Darrel

Surely you’d have to add an insane amount of ferts to cause a 1200ppm increase in TDS though Darrel? I once accidentally triple dosed EI level ferts, and it only added about 100ppm (from memory).
 

jaypeecee

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I did think my TDS meter was at fault, but with a solution of 1 liter RO water and 0.5 gram of table salt the TDS comes out around 550 ppm.
Hi @MichaelJ

I didn't comment on your statement above but I would expect a TDS figure around 500 ppm with the solution you made up. This tallies well with your measurement so I think you can safely say that your TDS meter is giving you a correct reading.

JPC
 

dw1305

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Hi all,
Surely you’d have to add an insane amount of ferts to cause a 1200ppm increase in TDS though Darrel?
My guess is that the levels have built up over the 8 months, probably mainly from the excess calcium (Ca++), sodium (Na+), chloride (Cl-) etc the ions that plants don't require or only require in small amounts.

cheers Darrel
 

dw1305

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Hi all,
Surely, the answer lies with the substrate, doesn't it? It's awash with fertilizers, isn't it?
I expect some of it is, but the plants will mop that up and it has been eight months? I've never used any nutrient rich substrates, so I don't have any practical experience of them.
Do a 80% water change, clean the substrate and everything else. Do another 80% water change.

Next week clean and 75%, weeks thereafter repeat!
That one.

cheers Darrel
 

jaypeecee

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I expect some of it is, but the plants will mop that up and it has been eight months?
Hi Darrel (@dw1305)

One thing we don't know is the depth of the substrate. If it's, say, 10cm depth, it could take a long time for all the ferts to leach out of it/be taken up by the plants, don't you think? As for how long, well, how long's a piece of string?

JPC
 

Wookii

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Hi Darrel (@dw1305)

One thing we don't know is the depth of the substrate. If it's, say, 10cm depth, it could take a long time for all the ferts to leach out of it/be taken up by the plants, don't you think? As for how long, well, how long's a piece of string?

JPC

As far as I understand it from Tom
Barrs comments on Eco Complete, it’s largely inert rock, and has very little in the way of ferts or CEC compared to, say, aquatic soils, or whatever their marketing department would like people to believe.
 

jaypeecee

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"Contains Iron, Calcium, Magnesium, Potassium, Sulfer plus over 25 other elements to nourish your aquatic plants.

Eco-Complete Planted Aquarium Substrate contains all the mineral nutrients needed for luxuriant aquatic plant growth without nuisance algae!"

Hi Guys,

So, does that mean the above isn't worth the computer screen it's written on? I guess we'll never know. I wait, with interest, to hear what the OP's comments are. Until then...

JPC
 

MichaelJ

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I really appreciate the feedback and welcome greetings. Thank you!

I am learning a lot here already.

So, in no particular order:

My impression is that the ECO-Complete substrate itself is inert, but the bag (the water or additives in the bag I supposed) contains a number of minerals and nutritions to get the initial growth started. But after 8 months I would expect the effect of that would be gone?

As for substrate depth, I would say both tanks got about a layer of about 3.5 inches (about 9 cm) - less in the front, and more towards the back.

I guess one way of figuring out the inertness of the gravel is to dig some up and let it sit in a bucket of RO water and see what happens to the TDS after a couple of days or a week perhaps?

I am definitely going with the recommendation of stop using the Acid and Alkaline Buffers and see what happens.

If its a buildup of sodium, chloride or calcium ( wouldn’t a huge buildup of Ca give me a very high GH reading?) or maybe potassium, then I suppose I just need to do some very large WCs, and perhaps do a bit less fertilizer from now on as suggested.

Another thing, I am filtering over Seachem Purigen and Matrix. I don't think that factors in, but just wanted to add that in case anyone was wondering.

Cheers,
Michael
 

MichaelJ

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The only other thing I can think is something is throwing off your TDS meter. Have you tried taking the TDS measurement in a glass of tank water, rather than directly in tanJust k?
Just tried this in one of the tanks. The TDS in a glass of tank water is 1563 and 1558 in the tank... I tested the TDS meter with a solution of 1 liter of RO water and 0.5 and 1 gram of table salt and it pretty much matches the expected values. I am getting around 550 and around 1200 ppm respectively. Close enough I would say (I suppose the meter, my scale, liter measure and water temperature, which ideally should be 25C for the meter, might be off by a bit, but the numbers seems fairly well in the ballpark for me to trust that the meter is not being too much off from what I except it to be... I probably wouldn't trust it for anything below +/- 50 ppm).
 
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dw1305

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Hi all,
If its a buildup of sodium, chloride or calcium ( wouldn’t a huge buildup of Ca give me a very high GH reading?)
Yes, if you had more calcium (Ca++) in your water it should show up on the dGH test. You will never get a huge build up of Ca++ ions, purely because of <"the limited solubility"> of most calcium containing compounds. Water is fully saturated with Ca++ and HCO3- at about 17 dGH/dKH, which is somewhere near 600 microS.

I don't know exactly how the dGH test kit works, I tend to use conductivity as a proxy for dissolved CaCO3 in natural waters, and it is easy to test for in the lab. with <"ICP, AAS or flame photometry">.

In practical terms all potassium (K), sodium (Na) and chloride (Cl-) salts are soluble.
then I suppose I just need to do some very large WCs, and perhaps do a bit less fertilizer from now on as suggested.
That would be my suggestion. As you've found out, from your meter checks, it isn't a huge addition of salts to raise the conductivity appreciably.

cheers Darrel
 
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jaypeecee

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My impression is that the ECO-Complete substrate itself is inert, but the bag (the water or additives in the bag I supposed) contains a number of minerals and nutritions to get the initial growth started.
Hi @MichaelJ

So, if I understand you rightly, there are two things in a bag of Eco Complete - the sand/gravel itself and a solution of nutrients. Is that correct? Is it a (small amount of) solution or is there evidence of solids (as powder or crystals) mixed into the inert substrate material? Does it contain organic matter?

JPC
 

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