# Walstad tank 1 year old, Qs about chemistry



## SBS (Feb 26, 2013)

Hi all,

I asked somewhere else but just couldn't get a conclusive answer.

I have a small Walstad tank setup like this for the last year.

You can see its current state on the video below. Please excuse the hazy glass. I haven't cleaned the tank in a year but the snails and shrimp like hanging on the glass and eat off the biofilm.






The tank has around 1 inch soil(Verve Fruit and Vegetable planter) mixed with 5-10% clay and a cap of about 1/2 inch of sand.

The tank is doing fine, the shrimp are fine, started the colony from 20-sh tiny shrimplets that fell off a sponge from another filter when I washed it, and they grew up in this tank from little dots.

However the stats of the tank have changed significantly over time and I would like to know if that's because I didn't do water changes for the last year(some scoops occasionally before top ups but very seldom) or because the soil lowered my stats?

The original Tap water the tank started with had the following readings:

TDS: 300-ish
Gh: 12
Kh:8
Ph:7.4

After a year the tanks readings are:
TDS: 200-ish
Gh: 7
Kh: 2
Ph: 7.4

I understand that the water has gone more acidic. I only recently checked the bag of soil I used in this tank to see what's written and apparently there is peat in it, hence making the water softer I suppose?
But is the TDS supposed to get lower as well? I haven't changed the water or cleaned, or even siphoned the tank for that period of time(not proud of myself) so shouldn't the TDS build up and register higher than it started with instead of getting lower? Where did the organics go? I feed daily? My TDS meter is fine because it tests what it should on my other tanks.

Also, I read in Diana Walstad's book once that peat and iron in the same soil(as in the red clay I mixed in the soil) can cause iron toxicity over time if the soil goes too acidic. Should I worry about this in time and how to prevent it?
I mean the tank has been doing great, but I suppose I should start doing regular water changes to prevent it from going more acidic? The critters have been doing great but they are cherry shrimp and snails so they won't like it very acidic I suppose....

I am setting up another 60l tank as a Walstad tank soon. I am going to use the same soil mixture so just want to make sure it can be safe long term? I may have some pygmy corys in it besides shrimp and snails.

Any ideas? Thank you for your time.


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## Wy Renegade (Apr 16, 2014)

Since your pH has remained the same (according to what you posted), I'm not quite sure of your question. At this point, your tank has not become more acidic, its current level of acidicity is the same as when you started, what has changed is your carbonate hardness, or your ability to buffer for pH changes. Thus far, no pH change has occurred - at least according to what you posted. The following is a good read for understanding the differences between pH, KH, and GH. You are correct in that your water is softer, but it is not more acidic, at least not yet.

http://www.chelonia.org/articles/waterchemistry.htm

Since TDS is a measure of all dissolved solids, both inorganic and organic, removal of organics substances will allow TDS to go down.


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## SBS (Feb 26, 2013)

> I'm not quite sure of your question.


Thanks for answering Wy.
My question is why is the TDS going down over time? I have not done water changes, vacuum or cleaning of any sort?

In regards to the Ph, yes it has remained the same. But from what I know a Ph is a measure of the ratio between H+ and OH- but one doesn't know how many of each one has in the tank no matter that the ratio maybe the same. For example in one tank a Ph may represent roughly speaking a ratio of 
H+:OH- of 100:40, in another tank the ratio maybe 1000:400, both will read exactly the same Ph because the ratio of these numbers is 10:4 but in one tank the amount of actual free H+ will be way higher than in the other causing it to be actually more acidic. 
Since my tap water has very good buffering capacity to start with and buffering capacity is the ability of the water to keep that ratio constant, then the ratio may have remained the same but it may have knocked more H+ and OH- over time on both sides of the ration thus making the water more acidic. Only on theory of course as I have no idea if that's what has actually happened but considering the TDS and Gh and Kh have gone down too?

That's why I don't think a Ph is an indicator of anything. For example if I never knew the history of the tank and one tells me the TDS is 200 and the Gh 7, irregardless of a Ph of 7.4 I would have said this is soft water.


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## Skizhx (Oct 12, 2010)

> In regards to the Ph, yes it has remained the same. But from what I know a Ph is a measure of the ratio between H+ and OH- but one doesn't know how many of each one has in the tank no matter that the ratio maybe the same.


pH is a measurement of the concentration of H3O+ (which is influenced by the amount of H+ in the solution, but is not the same thing). Water is an equilibrium (H3O <-> H2O <->OH). The more H+ in solution, the more H3O, the more acidic the solution.

Hardness in water acts as a buffer. Explained simply, buffers act as a sink for OH- and H+, so they are not freely available to shift the H3O<->H2O<->OH equilibrium.

So basically no, your tank is not more acidic, and pH is the only measurement you need to determine the acidity.

Regarding GH and KH, your plants are using these for micronutrients, which may be part of the drop.

However, as your substrate is decomposing it produces acidic compounds.

I *think* that the acidic compounds create an environment in the soil that's acidic enough that some of the Ca and Mg form precipitates.

Or maybe it's an ion exchange of hydrogen in the acids for Ca/Mg?

I'm probably wrong on both guesstimations, so I'll just say that what you're seeing isn't abnormal, even though I can't put my finger on the exact mechanisms responsible.


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## Tugg (Jul 28, 2013)

If you are toppi g off with RO water, then your TDS is dropping due to precipitation and micro nutrient consumption. The decome process will also create acids that will neutralize your kH over time. Additionally, if CO2 gets low, some plants consume CO3 as a car on source, again lowering kH. Lastly, many microorganism also consume kH.

I'm actually surprised you have any left. Did you mix in a CaCO3 source like oyster shells or crushed coral with the soil?

Be careful as it drops. Once the kH gets exhausted your pH will start dropping and can reach un healthy leaves. Without any buffer pH crashes are a real concern.


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## Wy Renegade (Apr 16, 2014)

Well, first of all a little disclaimer here as I'm a bit out of my depth - chemistry is not my strong suit. While you are correct in that pH is in fact a measure of the ratio of hydrogen to hydroxyl atoms, having a ratio of 100:40 or 1000:400 doesn't allow for a change in the level of hydrogen ion activity, and therefore doesn't change the acidity of the water. 100 free ions or 1000 doesn't matter because the activity level of the free ions is balanced by the appropriate ratio of free ions of hydroxide. Now anybody is free to come along and tell me that I'm incorrect in that understanding. 

What I'm not following is that you are somehow equating a decrease in Kh (which is a measure of carbonate hardness) with an increase in acidity. A drop in Kh does not imply an increase in hydrogen ion concentration. It implies a decrease in the buffering capability of the water itself - buffering can be accomplished by any ion that will bond with the free hydrogen or hydroxyl ions to prevent a change in the concentration of free ions. Salts (i.e. ions) in saltwater for example increase the Kh and GH of water and increase its buffering capacity, but they don't change the acidity of the water. In other words, the fact that water is salt water and has a higher Kh and GH doesn't make it more basic. The fact that your Kh has dropped indicates that your buffering ability has declined, but that doesn't necessarily mean that you concentration of H+ or OH- ions have increased or decreased. Again, feel free to tell me that I don't know what I'm talking about if I am incorrect. A change in water hardness does not equate to an increase or decrease in acidity or an increase or decrease in hydrogen and/or hydroxyl ions.

TDS is a measure of total dissolved solids and is not directly related to chemical changes. I can have muddy water that has an extremely high TDS, that doesn't mean it has more ions of any type, that is simply a result of the inorganic debris that is floating in the water. On the other hand I could have a very basic solution and TDS could be 10.

A drop in Kh means that you are losing ions of some sort - that could be a result of the uptake of ions by living organisms. While a drop in TDS simply means you are losing dissolved solids - could be resulting from a drop in organic debris as bacterial activity increases.

Gotta be honest, I'm just speculating based on my fairly limited understanding of the chemistry here. To my knowledge measuring and following these chemical levels in freshwater is a bit different than in an aquarium with saltwater. With saltwater, we pretty much control all the chemicals in the water through additives in the form of the salt we add to the water. In freshwater, with tap water, we don't control and therefore we don't actually know what is comprising those numbers in the initial tap water or in the tank.

Hopefully someone with a little stronger knowledge of chemistry can help out here.


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## Skizhx (Oct 12, 2010)

My chemistry is rusty. 

pH is a measurement of H+ concentration. Was a bit confused about things when I said H3O. Just correcting myself.


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## nickmcmechan (Mar 23, 2014)

Have just read Diana Walstads book, I would say all you need to do is get a little crushed oyster shell (or similar) in there and do a small water change, start off with a small one, say 5% as you haven't done one for a year


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## SBS (Feb 26, 2013)

Thanks for your thorough explanation everyone. It's really helpful.



> If you are topping off with RO water, then your TDS is dropping due to precipitation and micro nutrient consumption.


I top up with tap water TDS 300, Gh 12, Kh 8, Ph 7.4



> I'm actually surprised you have any left. Did you mix in a CaCO3 source like oyster shells or crushed coral with the soil?


No, I forgot to do it in this tank and left it without. I have another tank with soil on which I did sprinkle dolomite under the substrate. I've started doing small water changes to increase the Kh some.



> What I'm not following is that you are somehow equating a decrease in Kh (which is a measure of carbonate hardness) with an increase in acidity.


No, I didn't mean that. I referred to the decrease of TDS and Gh mainly over time. I seem to be using the term "acidic" incorrectly. I mean water is becoming soft. Do you mean that a water becoming soft doesn't mean it's becoming acidic?



> I can have muddy water that has an extremely high TDS, that doesn't mean it has more ions of any type, that is simply a result of the inorganic debris that is floating in the water. On the other hand I could have a very basic solution and TDS could be 10.


I have a couple of questions in regards to this.
I understand that the TDS is a measure of the total dissolved solids however the TDS meter we use test conductivity, hence the ions in the water?
In regards to low TDS of 10ppm for example and basic water.
If my water has a Gh of 7 for example. Then wouldn't the TDS be at least 7x17.86=125 ppm roughly. Isn't the TDS a collective of all compounds including Ca and Mg plus other solids I haven't measured or can't measure separately? A TDS of 10ppm means there is barely any Gh to start with? So my limited understanding is that although not directly related, I can't have a TDS of 10 in my lets say basic water with a Gh of 10? Or can I?



> So basically no, your tank is not more acidic, and pH is the only measurement you need to determine the acidity.


I am ignoring what the Ph value itself is because I see that despite the value the rest of the stats are totally different from what they were. I understand the buffers have done well to keep the Ph the same as it was originally. Just the other bits of the changes interest me too.

Thank you again everyone.

Just one more question. Is it possible to have snails with badly degrading shells in water with TDS of 500, Gh 14, Kh 5 and Ph of 7.4? Because I have this happening in another tank?

Am I lacking calcium in this tank with a Gh of 15 although the tank glass on all my tanks has calcium deposits including the affected one? Do I only have Mg in that Gh then or what do you guys think?

I've never had this happen before and I thought if it would happen it would be in the single tank in which the water has become softer over time but it's in tank in which the stats have gone the other way up. It's a plain sand 60l planted tank with one platy, shrimp and snails. The shrimp and the fish are doing well and I have baby shrimp so they are still multiplying despite that the snails are dying? That's the tank I am going to tear apart and put soil in as well. Obviously I don't want snails with white decomposing shells again. Poor things. I've added a piece of dead coral for more calcium, doing water changes with my hard tap water. I'll see if that solves the problem. I just can't understand why is it happening? Where did all the calcium go?

On another hand I have another planted soil tank with a TDS of 500-ish, Gh 14, Kh 4 and ph of 7.4 in which the snails are perfectly happy.

Sometimes I think I should just throw those tests in the bin because they don't add up.


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## Wy Renegade (Apr 16, 2014)

SBS said:


> No, I didn't mean that. I referred to the decrease of TDS and Gh mainly over time. I seem to be using the term "acidic" incorrectly. I mean water is becoming soft. Do you mean that a water becoming soft doesn't mean it's becoming acidic?


Quite right; soft does not equal acidic, but a drop in TDS and Gh does mean water is getting softer.



SBS said:


> I have a couple of questions in regards to this.
> I understand that the TDS is a measure of the total dissolved solids however the TDS meter we use test conductivity, hence the ions in the water?
> In regards to low TDS of 10ppm for example and basic water.
> If my water has a Gh of 7 for example. Then wouldn't the TDS be at least 7x17.86=125 ppm roughly. Isn't the TDS a collective of all compounds including Ca and Mg plus other solids I haven't measured or can't measure separately? A TDS of 10ppm means there is barely any Gh to start with? So my limited understanding is that although not directly related, I can't have a TDS of 10 in my lets say basic water with a Gh of 10? Or can I?


Quite right, I misspoke on this one, can't have basic water with a low TDS. However since TDS is a measure of ions, I can have a high TDS that does not necessarily have a high concentration of calcium and/or magnesium. That high TDS could come from organic ions, salts, or metals, none of which will affect your pH value.



SBS said:


> I am ignoring what the Ph value itself is because I see that despite the value the rest of the stats are totally different from what they were. I understand the buffers have done well to keep the Ph the same as it was originally. Just the other bits of the changes interest me too.


understood, but again, you can't have a change in acidity without a change in pH.



SBS said:


> Just one more question. Is it possible to have snails with badly degrading shells in water with TDS of 500, Gh 14, Kh 5 and Ph of 7.4? Because I have this happening in another tank?
> 
> Am I lacking calcium in this tank with a Gh of 15 although the tank glass on all my tanks has calcium deposits including the affected one? Do I only have Mg in that Gh then or what do you guys think?
> 
> I've never had this happen before and I thought if it would happen it would be in the single tank in which the water has become softer over time but it's in tank in which the stats have gone the other way up. It's a plain sand 60l planted tank with one platy, shrimp and snails. The shrimp and the fish are doing well and I have baby shrimp so they are still multiplying despite that the snails are dying? That's the tank I am going to tear apart and put soil in as well. Obviously I don't want snails with white decomposing shells again. Poor things. I've added a piece of dead coral for more calcium, doing water changes with my hard tap water. I'll see if that solves the problem. I just can't understand why is it happening? Where did all the calcium go?


Possibly though this is a bit harder to interpret - keep in mind that general hardness isn't a measure of just calcium and magnesium - it also represents other ions, so while unlikely you could have a high TDS and Gh that doesn't necessarily indicate a level of calcium ions. It will be interesting to hear what happens with your coral "experiment."


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## SBS (Feb 26, 2013)

> It will be interesting to hear what happens with your coral "experiment."


I think it's looking good. Done 3x50% water changes since I noticed along with adding the dead coral. I'll let you know.
Are the snails with damaged shells going to recover if water is right or they are gonners once the shell is damaged a bit? Their shells are whitish, some corroded a bit but still there, at least the ones that aren't dead or the ones I saw.


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## SBS (Feb 26, 2013)

Well I think between the coral and a good few big water changes I've sorted the snails. I took the coral out. I think the pond snails were the most affected and some of the Malaysian but not all. There are also rams horns in there that looked fine all along so it seems it affects them differently. I find it very odd because the stats read very hard water in this tank.
Anyways, it's back to normal it seems to me.
It never affected the cherry shrimp and the one fish in there is a grown up baby platy that travelled to the tank on a plant leaf and looks quite healthy to me.
I'll be taking this tank apart soon anyways once the soil is mineralized.


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## Phoenix1307 (Jun 1, 2014)

I would point out that peat moss in the soil in very unlikely to be having any effect on the water itself, otherwise you'd also be getting tannins in the water, and would to have been changing it regularly, otherwise it would look like Coca Cola had been poured into it by now, LOL. So, it's equally likely that the peat moss is not responsible for the softening of the water. Watstad does report that a soil tank will tend towards neutral on its own, though I don't remember the chemistry behind that.


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