Measuring buffer capacity of water? - The Planted Tank Forum
 
LinkBack Thread Tools Display Modes
post #1 of 5 (permalink) Old 03-23-2018, 06:57 AM Thread Starter
Algae Grower
 
PTrader: (0/0%)
Join Date: Mar 2018
Posts: 20
Question Measuring buffer capacity of water?

When I check the TDS of a strong buffer solution (calibration solution for example) it is over 1000, whereas untreated water is under 100 (4.4 pH well water). Based on this data, one might surmise that there is a correlation between TDS reading and buffering capacity. This is logical because buffers are composed of conjugate acid/base pairs, which are made up of anions which register on the TDS meter? Does that sound right?

If I remember my chemistry correctly, the preferred way would be to do a titration with a colored indicator such as phenothalien, which would then show how much base of a known molarity is needed to neutralize the acidic buffered water; I would imagine however that most other people on here don't do it that way.

So what is the preferred way to measure buffering of water by aquarists? Is there a meter for that, or a way to co-opt some other meter to work for this?

Thanks
cds333 is offline  
Sponsored Links
Advertisement
 
post #2 of 5 (permalink) Old 03-23-2018, 11:14 AM
Planted Tank Guru
 
Maryland Guppy's Avatar
 
PTrader: (15/100%)
Join Date: Dec 2014
Location: Arnold
Posts: 3,684
dKH for carbonate hardness/alkalinity.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Growing is not that difficult.
Maryland Guppy is online now  
post #3 of 5 (permalink) Old 03-23-2018, 01:12 PM
Planted Tank Enthusiast
 
KevinC's Avatar
 
PTrader: (6/100%)
Join Date: May 2004
Location: Oshkosh, WI
Posts: 738
kH is alkaline buffering capacity - the test assumes a starting pH above about 5.5 and you titrate it down with acid. This is the pH at which almost all bicarbonate is converted to carbonic acid.

Since you are starting with a pH of 4.4, you would measure 0 kH. Is that a degassed pH where you left the sample out overnight before taking the reading? It is unusual for wells to be that acidic.

Kevin

Kevin

72g bowfront planted, CO2, 4x - T5HO, Eheim 2213 and 2217, 2 angels, pristella tetras, blue tetras, betta, albino bristlenose pleco, albino cories. Sword, vals, hygros, ludwigias, java moss and fern, anubias

2g Mac-quarium. Clown gravel, fluorescent plastic plants, and 2 guppies.
KevinC is offline  
 
post #4 of 5 (permalink) Old 03-24-2018, 07:54 AM Thread Starter
Algae Grower
 
PTrader: (0/0%)
Join Date: Mar 2018
Posts: 20
Question

This is what I am unclear on- I am aware of the KH test, however that only tests for carbonate, while there are many other buffers that are not carbonate. Seachem makes phosphate buffers specifically because they are more stable than carbonate. Why is alkalinity only based on carbonate then?

You are correct that it tests as 1 degree KH (cant test with 0 drops).

The pH rises to around 5 when degassed.

I realize that 4.4 is unusual, but as I understand it, it is only unusual if is buffered (because in unbuffered water you can easily reach a very low pH with relatively little acid).
cds333 is offline  
post #5 of 5 (permalink) Old 03-24-2018, 04:03 PM
Planted Tank Guru
 
Zorfox's Avatar
 
PTrader: (5/100%)
Join Date: Jun 2012
Location: Gainesville, FL
Posts: 2,105
Quote:
Originally Posted by Maryland Guppy View Post
dKH for carbonate hardness/alkalinity.
This is correct.

Alkalinity and PH obviously have a direct relationship. However, as you've noticed there are other buffers such as phosphates. The KH measure hobbyists use is more of an approximation of buffer capacity. It's not an actual measure of buffering capacity.

KH is a measure of calcium carbonate (typically CaCO equivalent) per liter of water, mg/l CaCO.

Buffer capacity is a measure of how much strong acid or base it takes to change PH one unit (up or down), moles/L.

Clearly two entirely separate measures. However, the predominant buffer found in water are carbonates. When we have a measure of carbonates we have a relatively close approximation to the minimum buffering capacity.

Quote:
Originally Posted by cds333 View Post
When I check the TDS of a strong buffer solution (calibration solution for example) it is over 1000, whereas untreated water is under 100 (4.4 pH well water). Based on this data, one might surmise that there is a correlation between TDS reading and buffering capacity. This is logical because buffers are composed of conjugate acid/base pairs, which are made up of anions which register on the TDS meter? Does that sound right?
There is a correlation between TDS and buffering capacity just like there's a correlation between the planet's gravity and coffee cups. If we added more cups (mass) the gravity increases which would indicate we could calculate the number of coffee cups based on current gravity right? Of course not!

In fact, PH is actually more of a theoretical measure anyway. Your PH pen does not exactly equal PH, [-log(H+)]. There is an effective hydrogen concentration to consider. Therefore, many present PH calculation as, PH = -log(H+ activity). This will correct any issues in calculations, right?. Unfortunately, principles of thermodynamics state that the activity of one kind of ion (e.g., H+) is unknowable. This invalidates the second formula leaving the original flawed based on ion activity.

I'm not trying to confuse you by pointing out the problems with PH. Instead, I am trying to illustrate that our aquariums are not theoretical models. Far too many people get tied up in the fine details and never look up to see the horizon ahead. Hobbyists should not have to be concerned with thermodynamics, chemistry, physics and god knows what else.
Zorfox is offline  
Reply

Tags
None

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the The Planted Tank Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome