Some handy facts about water

[dw1305]

Hi all,

.......... using TDS units is still an unnecessary detour from what we measure to something we can only estimate.

Perfectly put.

Beside that, if we suddenly begin using "better" units, there would appear trouble with reading all what had been written before that glorious day. I think UK residents have encountered it quite recently with departure from pounds and ounces to kilograms and grams.

There is <"truly no hope for us"> in the land of the <"pole, perch"> and <"groat">.

cheers Darrel

 

[LMuhlen]

Something that I miss in articles about water parameters is an explanation as to why this subset of ions, the multivalent ones, or even the bivalent ones, is relevant for us and why are they grouped together. What makes Ca and Mg, measured together, more relevant for plant or fish keeping than other ions. Why do most people seem to think it is important to prepare the water for a water change in a way that there is no GH shock, while they don't seem to care about a K or NO3 shock? What makes these ions seen as more than just another fertilizer?

In other words, I understand what GH stands for, but I don't understand what is so important about it. I sometimes think it is purely because it is apparently simple to measure, so it is the tool that we have at hand.

As for alkalinity, it seems important for its effect on pH, but carbonates also seem relevant for plant keeping, and are mostly avoided. Other ions presented as a subset of alkalinity, such as phosphates, are treated as fertilizer. What makes carbonates undesired? What are their characteristics other than affecting the pH?

 

[Oldguy]

I think UK residents have encountered it quite recently with departure from pounds and ounces to kilograms and grams.

In 1896, the British Parliament passed the Weights and Measures (Metric System) Act, legalising metric units for all purposes but not making them compulsory.

UK drinking water reports from water supply companies use ppm/mg per litre and degrees Clark and degrees French. Test kits for the home aquarist use the German scale for some reason.
The Clark & French units are for a guide to laundry powder/solution usage. They and the German unit are as you rightfully note are a tad large for aquarist use.

As I said, just a mess

Its just an industry standard. It keeps the numbers small, though I doubt there are many who know what their drinking water analysis is, we have taken 'safe to drink' as a given for many generations.

Personally for chemical calculations there is a lot to be said for moles and its sub-units. However I still prefer ppm for aquarium management.

On a personal note I would still like fine single malt whisky to be in bottles with the volume molded into the glass in Imperial fluid ounces. Even the empty bottles are becoming collectors items.

 

[_Maq_]

What makes Ca and Mg, measured together, more relevant for plant or fish keeping than other ions.

Nothing. It's merely a tradition. In water processing report it's featured mostly for water processing relevance - Ca and Mg tend to form precipitates in plumbings. Beside that, calcium affects the taste of drinking water, mostly positively. Calcium-free water is considered less 'tasty'.

What makes carbonates undesired? What are their characteristics other than affecting the pH?

I've mentioned it in the original post. Bicarbonates negatively affect some enzymatic functions within plants. It's been described in detail in agronomic literature. On calcareous soils, plants are sometimes able to take up iron, yet unable to assimilate, utilize it (for chlorophyll formation). Various species differ in their degree of adaptation to elevated bicarbonates.
In practice, we have seldom any means to distinguish the effects of pH from those of bicarbonates because it's quite difficult to change the former without affecting the latter. There's one significant exemption to that - CO2 injection. With that, you can decrease pH while keeping bicarbonates quite high. I suspect this may be of relevance in some cases but I don't inject CO2 and thus cannot perform any experiments.
One 'suspicious' example: This year, I've performed an experiment with Bacopa lanigera. This plant is often reported to be very difficult, even unfit for submerged vegetation. My results were different: it's very easy, only demanding acidic water (preferably below pH=6.0) with very low bicarbonates. With CO2 injection, you can push pH down to 6.0 while keeping alkalinity above 1 or 2 °dKH. And that, I suspect, may be the difference.

 

[dw1305]

Hi all,

It's merely a tradition. In water processing report it's featured mostly for water processing relevance - Ca and Mg tend to form precipitates in plumbings.

That is it, all to do with <"scale formation">, detergent foaming and <"brewing">.

Beside that, calcium affects the taste of drinking water, mostly positively.

Personally I much prefer <"hard water to drink">.

As for alkalinity, it seems important for its effect on pH, but carbonates also seem relevant for plant keeping, and are mostly avoided. Other ions presented as a subset of alkalinity, such as phosphates, are treated as fertilizer. What makes carbonates undesired? What are their characteristics other than affecting the pH?

What makes Ca and Mg, measured together, more relevant for plant or fish keeping than other ions

They go together as answers, it is to do with the nature of freshwater and the organisms that live in it, both plants and animals.

Rain water is naturally "soft", it has been distilled and doesn't have (m)any solutes present, other than dissolved atmospheric gases. Water is a very efficient amphoteric solvent, which means that <"it picks up ions"> from any compounds that are soluble in water, weak bases or weak acids. If that rain falls on a river catchment without (m)any bases, such as the Rio Negro basin, that water remains very low in ions ("poor in minerals") in the rivers etc, but it may pick up tannic and humic substances from leaf litter, peat soils etc.

The end result is water that is very low in nutrients, bases and bacteria. <"Plants and animals that have evolved in this water"> are very efficient at extracting the few bases that are present, but have little resistance to disease and may show hypercalcinosis in harder water.

By far the most frequent compound soluble in water is limestone (CaCO3) and limestone catchments will produce hard water with high Ca++ and 2HCO3- content. <"Plants and fish adapted to hard water"> may struggle in soft water, but normally this is less of a problem, because it is much easier to add things to water than to try and take them away.

cheers Darrel

 

[sparkyweasel]

Test kits for the home aquarist use the German scale for some reason.

The first ones widely available were made by the German company, Tetra.

 

[MichaelJ]

I can see there's a localization issue here.

As for electric conductivity (EC) and total dissolved solids (TDS) question, I can report proudly that this is one of the few points where hobbyists of my country are somehow ahead. In ours, nobody pays attention to TDS and all understand that there are actually no TDS meters, only EC meters. While I appreciate the arguments presented by @MichaelJ and others, using TDS units is still an unnecessary detour from what we measure to something we can only estimate.

Hi @_Maq_ While I do appreciate the appreciation mentioned above, I also think there is a slight misunderstanding and I do not think there is a localization issue here. Yes, all consumer grade TDS meters inherently measures Electric Conductivity (EC), it just happens that many do not read it out as such, but instead only (or by default) reads out TDS - I think it has a lot to do with the fact that by far most that buys these devices apply it for their pools, spas/hot tubs, tap water, water softeners, water purifiers, dietary beverages etc. which all comes with documentation and online referrals that references TDS... However, whether it reads out in TDS, mho/cm, uS/cm (Siemens/meter is the actual SI unit btw.) or some other esoteric unit, is not taking away from the fact that it's an invaluable helpful aid to gauge the condition and stability of your tank. I for one would like to hear an argument to the contrary... When UKAPS elevate a post to being sticky it should, at least, be accurate and grounded... Telling visitors - of which most are non-experts and just infrequently popping in to seek advice on their tanks - that measuring TDS should be discouraged is a mistake in my opinion and not an advice I will follow.

Cheers,
Michael

 

[Hufsa]

Telling visitors - of which most are non-experts and just infrequently popping in to seek advice on their tanks - that measuring TDS should be discouraged is a mistake in my opinion and not an advice I will follow.

Very much second this. Its one of the few things that are reasonably straight forward to test, and is a cheap tool to help each user monitor their tank. Sure it has an unfortunate name that isnt entirely accurate, but there are many such cases in the world. I dont think the name should exclude the use. Guides on UKAPS should reflect the general view of the forum as much as possible, and a lot of us have a "TDS" meter.

 

[dw1305]

Hi all,

Telling visitors - of which most are non-experts and just infrequently popping in to seek advice on their tanks - that measuring TDS should be discouraged is a mistake in my opinion and not an advice I will follow.

I think there are two different arguments here. I have been, and I'd guess always will be, a fan of <"conductivity as a measurement">.

That was partially why I started using a datum <"conductivity range">. Conductivity isn't the most useful measurement, but it has certain advantages, because the meters are,

• <"relatively cheap">,
• <"plug and play">, you can just dip them in and get an accurate reading (but you may have to turn off your filter etc. )
• They don't have <"any consumables">, like pH meters do.
• They don't need continual recalibration, and you can make up your <"own calibration solutions">, and
• conductivity is a <"linear scale from RO to sea water">.

The issue for me, and I'll be honest I don't think it is a deal breaker, like @_Maq_ says, comes when we subsequently report those conductivity values (in microS) as <"ppm TDS">.

using TDS units is still an unnecessary detour from what we measure to something we can only estimate.

Because "TDS meters" actually measure electrical conductivity and then <"use a conversion factor">, either 0.5 when it is assumed that most of the ions are Na+ and Cl-, or 0.64 when it is assumed that most of the ions are Ca++ and 2HCO3- (ions with higher valency are better conductors of electricity), to estimate ppm TDS.

We need to know what the conversion factor was, and how warm the solution was (ions conduct more electricity at higher temperatures) before we can interpret that ppm TDS value.

cheers Darrel

 

[JoshP12]

I like TDS … and pH … .

Neither are gospel but all good proxies for “something going on” or “something staying stable - ish”.

They are pieces of the larger puzzle that we can use as information for diagnosis or to inform next steps.

 

[dw1305]

Hi all,

I like TDS … and pH … . They are pieces of the larger puzzle that we can use as information for diagnosis or to inform next steps.

Accurate measurement of pH would be more useful then accurate measurement of conductivity, but the difference in practice is that conductivity meters are a lot more plug and play than pH meters and conductivity is a linear scale, <"while pH is both a log10 scale and a ratio">.

If some-one reports a conductivity reading you can be pretty sure it is about right, but you are a lot less sure for a pH reading.

cheers Darrel

 

[jaypeecee]

Neither are gospel but all good proxies for “something going on” or “something staying stable - ish”.

Hi @JoshP12 & Everyone,

And that's why I use an ORP* meter as a proxy to provide an indication of TOC**. But, it's a slow (and expensive) process accumulating data. Nevertheless, my pursuit continues. The expense arises because of the need to involve a Test Laboratory to carry out the TOC measurement.

* ORP = Oxidation-Reduction Potential
** TOC = Total Organic Carbon

JPC

 

[MichaelJ]

I like TDS … and pH … .

Neither are gospel but all good proxies for “something going on” or “something staying stable - ish”.

They are pieces of the larger puzzle that we can use as information for diagnosis or to inform next steps.

Hi @JoshP12 Very well put. Its a gauge for stability... I personally don't measure pH much - and every time I do it comes out around 6.4-6.7'ish (I run low-tech tanks). With proper maintenance I don't see a whole lot of reasons why my pH would not be reasonably stable (misconception ?) - Ok, if I completely mess up by over-dosing KH2PO4 when I prep my RO water I could get into trouble, but that would show up on my TDS meter anyway when I gauge the mixing containers (unless I countered it by equally messing up and under-dose some other compound).

And that's why I use an ORP* meter as a proxy to provide an indication of TOC**. But, it's a slow (and expensive) process accumulating data. Nevertheless, my pursuit continues. The expense arises because of the need to involve a Test Laboratory to carry out the TOC measurement.

Hi @jaypeecee, Remember I got a MW500 ORP meter a while back. I seem to always measure around 300 mV in both tanks. its been a while since I measured though. I travelled a lot over the spring/summer and had to put the hobby a bit on the back burner, but I still measured around 300 mV on the few instances where I thought I had neglected my tanks in terms of maintenance (for instance I only did one WC for 5 straight weeks between mid May and mid June, but had someone to top off the water and of course feed the livestock). I measured ~290 mV (only slightly lower than "normal"), but my TDS rose quite significantly in both tanks in the same time frame. Of course, this is all anecdotal and I do remember we discussed my somewhat "strange" readings and that I perhaps got a faulty MW500 unit. In any event, ORP/TOC are not easy topics.

Good to see you back btw.

Cheers,
Michael

 

[MichaelJ]

Accurate measurement of pH would be more useful then accurate measurement of conductivity

Hi Darrel, I would like to understand this bit better - can you elaborate a bit on this.

Cheers,
Michael

 

[JoshP12]

Hi all,

From a practical side, I wanted to share what just happened.

So I look at my tank - and anyone who has been following the journal knows that I literally threw Pandora’s box into it and have been watching.

So it looks crazy, green, cloudy, beautiful plant structures despite this.

And I haven’t changed the water in several days almost a week - so I look at the top near the weir and there’s some suds (some kind of organic).

My pH checks out at “stable” and “where it should be” and my tds is within 15 -30 of water change ish tds in ppm.

Neither of those is alarming - I’ve easily run within 30 points of tds with no issues.

But the trigger for me to know to change water and do some maintenance isn’t the tds or the pH as both indicate it’s fine — it’s looking at the tank. Even though plant forms are fine - it’s time.

So I don’t think anyone should be using any one of these observation/data collectors in a vacuum.

 

[Hufsa]

So I don’t think anyone should be using any one of these observation/data collectors in a vacuum.

Definitely not
There is no substitute for looking at the total picture and getting to know your tank.
I follow my instinct more and more with my tank and it seems to work out pretty well based on how vague the feeling can be sometimes.

 

[MichaelJ]

So I don’t think anyone should be using any one of these observation/data collectors in a vacuum.

100% Agree! 👍The most valuable gauges we have is our eyes and good judgment... the latter comes with experience.

Cheers,
Michael

 

[dw1305]

Hi all,

I would like to understand this bit better - can you elaborate a bit on this.

pH
<"Ideally we would like to know"> both the <"pH of the water"> and the degree of carbonate buffering. This is the <"ANC4.5 value"> that @_Maq_ talks about.

If we don't know the alkalinity of the water? A pH value of pH8 could mean <"our water has 17 dKH">, or it could mean it has very few anions other than 2HCO3- and it only <"has ~2dKH of buffering">.

in fact, alkalinity or acid neutralizing capacity (ANC) refers to the amount of strong acid needed to change pH from current value to a different (lower) value.
ANC4.5 is used regularly in water processing plants’ reports, and it denotes ANC to reach pH value of 4.5 – which is a point where no bicarbonate ions (HCO3-) remain in water.

The ANC value would give us a much better summary of whether our water is basic or acidic and whether the conditions are suitable for certain plants and animals: <"Corydoras in hard water...">.

The other problem is that <"pH values around neutral (pH7)"> are difficult to measure accurately and that the <"ratio of dissolved oxygen to dissolved CO2 has a large effect on pH">. Add in the <"technical complexity of pH meters"> and there are a lot of moving bits to line up.

Conductivity
The problem with conductivity is that it just represents the water's ability to conduct electric current, and that ability is linearly related to the number of ions (charged particles) in the water, but it doesn't tell you anything about the composition of those ions, they could be Na+ & Cl- or they could be Ca++ & 2HCO3- or <"a mixture etc">.

The advantages are that, in the UK, we can normally assume that:

• The conductivity of the water is directly related to its calcium carbonate (CaCO3) content, although this may not be true of <"other regions of the world">.
• <"Conductivity meters"> are very straight forward to use and measure a linear scale.

cheers Darrel

 

[palcente]

This formula gives bonkers results for low KH.





Matt

 

[Ria95]

This formula gives bonkers results for low KH.



Matt

LOL. Low - high; high -low it’s all bonkers.

As no references apart from a few wikipedia pages are given (apparently the author discovered all himself) it’s hard to say where things broke apart. So just assume failure in copypasta from some uncredited work and the fix is to multipy alkalinity by 0.35665 instead of dividing by it. So the estimation should be :

=A*0.35665*(10^(6.35-pH))*44

I’ll keep my opinion about the rest of the article to myself and leave to the readers and moderators to compare to the standard set by other excellent articles found on this nice forum, such as Ceg’s EI articles published 14 years ago.