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Anyone using APC bromothymol blue in drop checker

Neil6

Neil6

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12 Dec 2020
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Location
Uk
Just swapped over to APC brand of bromothymol blue but it seems the mix is too strong? VERY dark blue, green, almost difficult to distinguish between them as so dark.
I've tried diluting it but it's not working like the "aquarium one" so it hit or miss on colour change.
I've tried the old one again and it fine.

No info on the web site, but it's made for scientific use not aquariums. I thought it was all the same stuff at 0.04%??

APC Pure | Product | Bromothymol Blue Indicator Solution

Buy Bromothymol Blue Indicator Solution from APC Pure Ltd, the UK's largest diagnostic manufacturer and chemical retailer for science, education and industry.
apcpure.com apcpure.com

Does it need dilution?
 

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Disaronno said:
How much of the bromothymol blue are you using? I only use 2-3 drops of that per drop checker mixed with 4dKH solution.
Click to expand...
Sorry not with yeah😕...2-3 drops of bromothymol mix with what?
4dKH is bromothymol blue?
 
Hi all,
Neil6 said:
2-3 drops of bromothymol mix with what?
4dKH is bromothymol blue?
Click to expand...
The "bromothymol blue" is just the <"narrow range pH indicator"> that <"changes colour"> dependent on the pH of the 4dKH solution. Have a read through <"How to check your drop checker....">

The 4dKH solution is usually sodium bicarbonate (NaHCO3), it is the HCO3- bit that is important because CO2 and HCO3- are the weak acid and weak base pair in the carbonate buffering system. From <"James' Planted Tank - Re-mineralising RO Water">
1.5g NaHCO3 in 25 litres of water = 2 dKH
1.8g KHCO3 in 25 litres of water = 2 dKH
1.2g K2CO3 in 25 litres of water = 2 dKH
Click to expand...

The relationship for pH and CO2 level was experimentally defined and is summarised in this chart

1642033248806-png.179850


cheers Darrel
 
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dw1305 said:
The 4dKH solution is usually NaHCO3, it is the HCO3- bit that is important because CO2 and HCO3- are the weak acid and weak base pair in the carbonate buffering system.
Click to expand...
Leant something there. I thought any 4dKH water would do.
 
hypnogogia said:
No, bromothymol blue is the indicator. You need to add 2-3 drops of it to 4dKH water to dilute it.
Click to expand...
Sorry I thought it was one of the same thing😆
So I can make it myself then add the my brom.blue to it.

Found this:

0.12 grams bicarb to 999.88 grams water to yield 1L 4 dKH solution. Then you'll need about a 0.1% bromothymol blue in ethanol indicator solution.
 
dw1305 said:
I don't know if alkalinity and carbonate hardness are the same thing in this case or not. I'm going to say not (but I don't know).
Click to expand...
The buffer has to be bicarbonate buffer in this case, not just any alkalinity. It is the ratio of the bicarbonate and CO2 which determine the pH and therefore the color of the indicator.
hypnogogia said:
I thought any 4dKH water would do.
Click to expand...
That is probably also true in the 99.9% of cases, there is not much other buffer than bicarbonate in the tap water.
 
Neil6 said:
0.12 grams bicarb to 999.88 grams water to yield 1L 4 dKH solution. Then you'll need about a 0.1% bromothymol blue in ethanol indicator solution.
Click to expand...
This recipe is good, although measuring exactly 999.88 gramms water can be challenging. And you don't need to be that precise anyway, pH is on log scale.

Just add 120 mg to 1 liter of water. If you don't have the scale for the 120 mg, you can make a 100x or 1000x concentrated solution and dilute it afterwards. For example, add 12 grams to 1 liter RO water (that will be 400 dKH), and dilute it 100x (10 ml to 990 ml RO water).
 
Neil6 said:
Then you'll need about a 0.1% bromothymol blue in ethanol indicator solution.
Click to expand...
1ml of bromothymol blue to add to it
Neil6 said:
0.12 grams bicarb to 999.88 grams water to yield 1L 4 dKH solution. Then you'll need about a 0.1% bromothymol blue in ethanol indicator solution.
Click to expand...
I assume not tap water, RO or deionised water to dissolve the bicarb?
 
The bromothymol blue solution is a faff to make and lasts a long time so I just buy it pre-made. I purchased 'Neutro 4dKH Bromo Blue' years ago and I'm still working through the original bottle. Note that adding the 0.04% solution (in presumably pure water although the spec sheet doesn't say) to 4dKH solution will slightly dilute the 4 dKH solution - this is only a problem for hyper-anal chem geeks. 😉 If you make your own 4 dKH water you need to add the bicarbonate to pure water (distilled, RO, RO/DI) and NOT tap water and DEFINITELY not aquarium water!

Also in the category of "you really didn't need to know this" there is an error in the derivation of most of the pH/KH/CO2 tables that has been widely propagated (including I believe in the one above). Good discussion here: Is the PH-KH-CO2 equation completely wrong?. I made a corrected table of pH values (reproduced below) and a guide to using colour-measuring apps to quantify how green the green is: Drop checker - Fireplace aquarium The reason you didn't need to know this is that the level of dissolved CO2 in aquarium water that supports both good plant growth and doesn't (appear to) harm livestock is pretty forgiving... you're probably fine with anywhere from 15 - 40 ppm CO2 so small differences in measurement (or calculation) aren't of much practical consequence.

1725662011605.png
 
Hi all,
hax47 said:
What is wrong with tap water adjusted (diluted) to 4 dKH?
Click to expand...
It would add some unnecessary uncertainty, you would need to measure the alkalinity of the tap water accurately, assume that all that alkalinity was from carbonates etc.

Starting with DI water and adding NaHCO3 etc is just a lot more straightforward.

Cheers Darrel
 
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