The Planted Tank Forum - Reply to Topic
Planted Tank Forums
Your Tanks Image Hosting *Tank Tracker * Plant Profiles Fish Profiles Planted Tank Guide Photo Gallery Articles

Go Back   The Planted Tank Forum > Specific Aspects of a Planted Tank > Fertilizers and Water Parameters > Calibrating Test Kits - for non-Chemists

Thread: Calibrating Test Kits - for non-Chemists Reply to Thread
Post Icons
You may choose an icon for your message from the following list:

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:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Additional Options
Miscellaneous Options

Topic Review (Newest First)
08-05-2014 10:00 AM
Originally Posted by Darkblade48 View Post
For general purposes, the API and Sera test kits seem to be reasonably reliable.

The most accurate ones I have used are made by LaMotte, but they are pricy.

Of course, with any test kit, once calibrated, you can expect a reasonable degree of precision. With more expensive test kits, you will get both precision and accuracy.
I use Lamotte test kits at work ( swimming pool shop) I may check them out.
08-05-2014 01:01 AM
Originally Posted by manlyfan76 View Post
What kit do ppl think is best for Nitrates? or should we use any kit with the help of the calibration?
For general purposes, the API and Sera test kits seem to be reasonably reliable.

The most accurate ones I have used are made by LaMotte, but they are pricy.

Of course, with any test kit, once calibrated, you can expect a reasonable degree of precision. With more expensive test kits, you will get both precision and accuracy.
08-04-2014 11:13 AM
manlyfan76 What kit do ppl think is best for Nitrates? or should we use any kit with the help of the calibration?
05-14-2014 05:28 PM
Beer This thread has been linked to recently and there were requests for pH calibration.

This link gives a description of a high range calibration solution using 1/2 tsp of borax to a pint of water at a known temperature. Somewhere around room temperature should be sufficient enough for the accuracy of these kits. There is also a link in the article for lower pH solutions.
07-11-2013 06:40 AM
R. David Jain
An alternate 4dKH recipe

Here are some instructions I wrote up for an alternate method to make 4dKH solution. I had two main goals in coming up with this method: The first was to avoid the need for accurate weighing equipment (in fact, there is no weighing at all in this method, just measuring volumes). The second was to have it work even if the baking soda is not "fresh"... so that it would be precise even using an already-opened package that may have absorbed some water. The answer to both these requirements was to start with a fully saturated solution of baking soda and dilute from there. Since the saturation concentrations of sodium bicarbonate in (distilled) water are well-defined and known, this should (and in my estimation DOES) give good results, without having to measure out small amounts of baking soda ("is my level teaspoon level enough? Is the soda too compacted? How do I measure out 2 grams and how much of that is water??"). After some science facts and preliminaries, I lay out the steps below. I didn't have the energy to make a separate "what you will need" section, so you may want to read through the instructions first and make a list (almost everything is something that most people, especially fish-keepers, will have around the house anyway). The steps are simple enough, if long-winded, and this level of precision really isn't necessary probably for most people, but it was fun to come up with, and gives me peace of mind knowing that my "4dKH" solution is accurate to a few percent, and I won't inadvertently gas my fish .

Without further ado...
Relevant solubility figures (in water) for sodium bicarbonate
(see full temperature range of solubility at:
69 g/L (0 C)
96 g/L (20 C)
165 g/L (60 C)
236 g/L (100 C)
Solubility vs. temperature is highly linear in the full range 0-100C relevant for liquid water, so one can interpolate
from these figures as needed. For example, interpolating the solubility at 25C using the data points for 0C and 20C
gives (solubility at 25C) ~ [96 + 5*(96-69)/20]=102.75 g/L, and this is close enough for our purposes.

Our goal in this process will be to reach a concentration of 120mg/liter NaHCO3. From Wikipedia (edited for brevity):
"An aqueous solution containing 120 mg NaHCO3 (baking soda) per litre of water will contain 1.4285 mmol/L of bicarbonate.
...Since one degree KH = 17.848 mg/L CaCO3, this solution has a KH of 4.0052 degrees."

"Water" throughout refers to distilled (or de-ionized) water.
Dilution ratios are given as (amount total final mixture) : (amount starting solution). So, "Dilute 2:1" means
mix 1 part starting solution with 1 part distilled water.

"1 Cup" here does not necessarily have to mean 1 8oz cup (though it could be). You can decide on exactly what size
"cup" you would like to use depending on your needs. Larger quantities mean a more accurate dilution, but more wasted
materials (baking soda and distilled water). I chose to use a "cup" size which was actually 3/4cup=180mL because I had
a 3/4 measuring cup handy.

Be sure to wash and thoroughly dry (tap water is fine for this) your mixing vessels at EACH STAGE of the dilution.
Because we will be diluting over several orders of magnitude in concentration, even a small residue of higher
concentration material from an earlier step (say, from re-using the mixing vessels) will throw off the final

1) Create a saturated solution of sodium bicarbonate. First mix 2cups hot water with enough baking soda to saturate the solution. You will know that it's saturated when no more of the powder can dissolve and any additional amount added falls to the bottom of your mixing vessel. Using hot water (distilled water heated on the stove) ensures that the solution is truly saturated. After dissolving, we will cool the water back to room temperature, allowing any excess to precipitate out. Do not heat the water too much (warm to the touch is fine)!! At high temperatures, the bicarbonate ions begin releasing C02 and water to form carbonate ions, which will throw off the calculations.

2) Cool the water back to room temperature. For me, this was 25C, so my calculations in the later steps are based on this number. Adjust your numbers accordingly. Using an electronic temperature probe (like one used for cooking) submerged directly in the water will help you tell when the temperature has finished dropping and give you a more precise final temperature reading than a wall thermometer or home thermostat.

3) Do an initial dilution of 2:1. I would suggest bottling and saving a large portion (1cup or more) of this initial dilution to use for making more 4dKH water in the future, without having to repeat steps 1 and 2). You probably want to use a coffee filter for this initial dilution to get out any precipitated bits of baking soda. By diluting 2:1, we ensure no further precipitation of the bicarbonate out of solution, even if the temperature drops. Be sure to label the concentration of this solution on the bottle based on your temperature reading and the 2:1 dilution!!

4) Assuming the temperature of your starting solution was 25C, after this 2:1 dilution, you will have a concentration of 51.375 g/L (one half the saturation concentration read-off or interpolated from the solubility information above, based on your solution's temperature after cooling). Let's get diluting! We need to dilute by an overall factor of [51375mg/L]/[120mg/L]=428.125 (adjust the first number on the left as needed).

5) Dilute in a ratio of 2:1 8 times (NOT counting the initial 2:1 dilution). Keep track of your dilutions!! I STRONGLY suggest you have a pad of paper next to you to check off each 2:1 dilution, to make sure you do exactly 8). After this, the solution will be at 6.69 dKH (=428.125/2^8*4dKH if the starting solution was at 25C... adjust this number according to your situation).

6) The final step requires some precision in terms of measuring volumes, but if you have a dropper that can measure 1mL, an API test kit with test tubes marked with a 5mL line, and a larger measuring cup that can measure a few hundred mL's at a time in increments of 10 (available in most bigger supermarkets' cooking sections), it shouldn't be too hard. We need
to take the 6.69dKH solution that we now have (or whatever you got based on your starting temperature) and dilute it down to 4dKH. In the following formula, replace 6.69 with whatever your number is. Defining x as the number of mL's of distilled water that we need to add, and Y as the number of mL's in your user-defined "cup" (you should have at this point exactly 2 "cups" of diluted fluid), with some simple reasoning we can derive the equation:
x= 2Y*(6.69/4 - 1)
Once you add this many mL of water to the 2 "cups" of solution you already have, the resulting mixture will be at 4dKH! We're done!! Now bottle that sh*t! (Small refillable bottles for toiletries or what have you can be bought at a well-stocked grocery or drug store).

7) Testing: When I tested my results with the standard API KH tester, it changed color at 6 drops (indicating a KH of between 5 and 6 degrees). You will probably get a similar "off" result. Do not worry! These tests are notoriously imprecise (or rather, they are precise enough for the needs of typical aquarists, but they are not lab quality). I got independent confirmation of this fact when I had my local fish store test a sample of water that I had just tested for comparison. Their result was 2.1dKH, while mine was 4dKH (to within the error implied by counting a discrete number of drops). I don't know for sure what method they were using, but it was likely more accurate than mine (based on the fact that they can afford, and have interest in owning, more accurate equipment, coupled with the fact that they quoted me a number to the first decimal place, whereas your standard kit "rounds" to the nearest whole number). So, this tells me that my kit probably tests a little high, meaning that my reading of 5-6 was really closer to the 4 we should expect. In the end, the real "proof" of this method is in the procedure. So long as we followed the steps correctly (and that basic science works), there should be no reason not to get the 4dKH solution we were expecting. Still and all, a "sanity" check at the end is useful, just to reassure ourselves that we didn't screw something up TOO badly . If your number is way different from 4, then you might have mis-counted dilutions, have an expired test kit, or run into some other unknown gremlin. Short of this, just go ahead and assume that the solution is what it should be.

Happy drop-checking! I hope some of you out there find this useful .
10-12-2012 02:13 AM
Mathman I think I should have read the previous post...I already had some API Ph test kit...I added 3 drops to the drop checker along with the KH solution and now I have a reading...thanks
10-12-2012 01:33 AM
Mathman Thank you very much for the instruction on how to make a 4dKh solution.

I just finished making it and tested the water with a new API KH test...perfect 4 degrees.

Now, I'll add some to my drop checker and stick it inside the tank. Should the color change in a few hours to indicate the level of co2 in the water?
09-29-2012 09:34 PM
Hoppy Standard pH solutions are much more difficult and complicated than the "salt" solutions this thread is about. If someone is a good chemist, and can design a kitchen measuring equipment way to make standard pH solutions please do so, and I will put them in the first post in the thread.
09-29-2012 02:23 PM
AquariumNoob Someone otta do one of these for Ph! :P. Bought a PH Pen which needs calibration, and ive got no access to any fancy stuff nor do i want to spend another 15$ On bottles of stuff for calibration.
09-28-2012 11:47 PM
Hoppy Of course you do need to add a pH indicator solution, but you don't add anything to change the pH of the water in the drop checker.
09-28-2012 10:53 PM
markstr Hoppy, here I found it. Does this sound Familiar ?

First buy or make a 4 dKH standard solution (consisting of distilled water and a tiny bit of baking soda only). There are several ways to make it, including

Fill the drop checker bulb about half full of this 4 dKH water, then add 2-3 drops of pH test kit reagent, one that is yellow at low pH and blue at high pH, such as the API pH test kit reagent.
09-28-2012 10:50 PM
markstr Thanks Hoppy for that info. I just thought I saw a while back you responded to something in regards to this and mentioned about 2-3 drops of PH solution to add. Probably didn't catch it right LOL .. So, I'll just use the made up 4dkh solution and see what kind of readings I get.
Thank you again ....
09-28-2012 09:58 PM
Hoppy Atmospheric CO2 is enough to make a 4 dKH standard reference solution be dark blue. Adding an acid to lower the pH would only introduce more inaccuracy. The only improvements I know of for drop checkers are:
Use a pH meter instead of the pH reagent.
Improve the time response of the DC by increasing the contact area between the tank water to trapped air, and the trapped air to DC solution, plus reducing the volume of the DC solution.
Both of those improvements are doable if you use a semi-permeable membrane instead of trapped air to separate the tank water from the DC water. But, it isn't an easy design to do, and have it work well.
09-28-2012 09:33 PM
markstr Question: once I have the 4dkh solution here, do I just add to the drop checker or would I add a low PH solution say a drop or 2 to get the Dark Blue color as well into the drop checker and then wait a couple of hrs for correct readings ? I know you mentioned (which makes sense) in regards to "What is Green" to the eye.

Originally Posted by Hoppy View Post
KH Test Kit
This method, compliments of Cardinal's Keeper (
(Note: You will need a whole gallon of distilled water to do this.)
1. Start with 6 cups of distilled water in a clean measuring container
2. Add 1/8 teaspoon Sodium Bicarbonate (baking soda, freshly opened) to the 6 cups of water and mix
3. Pour out 3 cups of this mix and discard
4. Add back 3 cups of distilled water and mix
5. Pour out 3 cups of this mix and discard
6. Add back 3 cups of distilled water and mix
7. Pour out 1 cup of this mix and discard
8. Add back 1 cup of distilled water and mix
7. Water comes out to a 4 dKH solution
8. To make a 2 dKH solution, mix one cup of the 4 dKH solution with one cup of distilled water.
9. To make a 1 dKH solution, mix one cup of the 2 dKH solution with one cup of distilled water.
07-16-2012 05:04 PM
Hoppy I have tried 2 drop checkers numerous times, with various KH fluids in them, hoping that would improve the accuracy. It never did. The basic problem is the difficulty in judging the color of the solution - a slight mistake in judging what is "green" makes a big mistake in the ppm of CO2 you think you have. I ended up the happiest when I used yellow as the desired color, and DIY CO2 so I could be sure I wouldn't ever have too much CO2. Then I just tried to keep the DC color yellow, which was relatively easy.
This thread has more than 15 replies. Click here to review the whole thread.

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

All times are GMT. The time now is 10:46 PM.

Powered by vBulletin®
Copyright ©2000 - 2015, Jelsoft Enterprises Ltd.
Copyright Planted Tank LLC 2012