# Where can i get a big bottle of drop checker solution??



## Sammy Islam (4 Dec 2020)

Can't seem to find a big bottle anymore, where does everyone get theirs? Or do you make it?

Thanks


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## GHNelson (4 Dec 2020)

100ml CO2 drop checker test solution - monitor levels of CO2 in your Aquarium | eBay
Aqua Rebell - CO2 Check - 30 mg/l - 250 ml - Aquasabi


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## AverageWhiteBloke (4 Dec 2020)

Yeah that's weird, I haven't dosed co2 for some time but when I did dc solution in big bottles was in abundance but now all the usual suppliers seem to be only doing 10ml bottles.


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## Sammy Islam (4 Dec 2020)

hogan53 said:


> 100ml CO2 drop checker test solution - monitor levels of CO2 in your Aquarium | eBay
> Aqua Rebell - CO2 Check - 30 mg/l - 250 ml - Aquasabi
> View attachment 157399


Nice one, i did see the first one on ebay but avoided it because i've never mixed it before. 🤣


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## Witcher (5 Dec 2020)

1.2 g of bicarbonate soda (available probably anywhere in food shops etc.) dissolved in 1000ml of deionised water will give you 40 dKH solution. Then mix 100 ml of that water with 900ml of pure DI water - it will give you roughly 4dKH solution for the fraction of "official" price.

This may help as well:
4dKH Solution


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## Surya (5 Dec 2020)

Aqua Essentials do a premixed 100ml version for £4 (or they used to).

Edit: £5, but currently sold out... Neutro Bromo Blue 100ml [4dkhB] - £4.99 : Tropical Aquarium / Fish Tank Plants for Sale, CO2 Sets, Fertilisers, and more - Aqua Essentials, The Planted Aquarium Specialists


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## Sammy Islam (10 Dec 2020)

I got my drop checker solution from ebay, the one you have to mix. The instructions say put 2ml of 4dk water in to drop checker and add 3 or 4 drops of bromo blue. Am i looking for a dark blue? Does it matter if its 3 or 4 drops? 

Can i not just add it to the whole bottle instead of measuring out a little bit at a time?


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## lazybones51 (10 Dec 2020)

I only add a couple of drops of bromo blue to 4k solution, it generally seems enough.


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## Sammy Islam (10 Dec 2020)

lazybones51 said:


> I only add a couple of drops of bromo blue to 4k solution, it generally seems enough.


Can you add "too much"


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## lazybones51 (11 Dec 2020)

Sammy Islam said:


> Can you add "too much"


Yes, from what I've read adding too much changes the dkh of the solution, affecting how it works.


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## Sammy Islam (11 Dec 2020)

lazybones51 said:


> Yes, from what I've read adding too much changes the dkh of the solution, affecting how it works.



I filled up drop checker just over half way and put in 4 drops which gave me a bright blue. Today at lights on it was green but nearly clear, so i'm guessing i have to put in a couple more drops to get it to the colour of the premade solutions (a lot darker)


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## Sammy Islam (16 Dec 2020)

I was wondering why my drop checker wouldnt go limegreen/yellow like it use to with the old solution. Turns out the 4dkh solution i ordered from ebay is actually 5dkh after testing with kh test, makes sense why my drop checker is darker green. 🙈

Found some bicarbonate of soda hidden at the back of the cupboard so will try mix my own tomorrow. Easiest way seems to be 0.3g to 500ml DI Water. Seeing as i have accurate scales does that mean i can half that 0.15g to 250ml DI to make a smaller batch of 4dkh water?


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## dw1305 (16 Dec 2020)

Hi all, 


Sammy Islam said:


> Turns out the 4dkh solution i ordered from ebay is actually 5dkh after testing with kh test


There is no way of knowing, but my guess is that this is the wrong way around, and that your test kit is reading 5 dKH in a 4 dKH solution. 

I'd think of it this way. You give me a £1 coin, and rather than accepting it is £1,  I weigh it, and say  "_it weighs as much as £2, so it is  actually £2" _and give you a  pound back.  What is more likely? That the coin is counterfeit? or that the scales are wrong?


Sammy Islam said:


> Found some bicarbonate of soda hidden at the back of the cupboard so will try mix my own tomorrow. Easiest way seems to be 0.3g to 500ml DI Water. Seeing as i have accurate scales does that mean i can half that 0.15g to 250ml DI to make a smaller batch of 4dkh water?


You can, but even with accurate scales you are likely to get a more accurate result using <"serial dilution">. I also think it should be 0.03g NaHCO3, it is really easy to get lost in the powers of 10, but @Manuel Arias breaks down the maths in  thread linked below.

Because NaHCO3 is really cheap to buy I would start with <"3g of NaHCO3 made up to 500 mL with DI water"> to give you a 400 dKH stock solution, and dilute from there.  

cheers Darrel


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## Sammy Islam (16 Dec 2020)

dw1305 said:


> Hi all,
> 
> There is no way of knowing, but my guess is that this is the wrong way around, and that your test kit is reading 5 dKH in a 4 dKH solution.
> 
> ...


Thanks Darrel, makes sense but doesn't explain why the drop checker is dark green rather than verging yellow, so that's why i would like to make my own solution to test. 

I can make a bigger batch, but the problem i have is mesuring out the water precisely. How do i do that? I only have general containers with 1/4L, 1/2L and 1L marks.


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## dw1305 (16 Dec 2020)

Hi all, 


Sammy Islam said:


> but the problem i have is mesuring out the water precisely.


Just by weight. Because water has a density of one,  a kilogram of water has a volume of one litre and  one gram  = one millilitre.  

Even in the lab. I use the scientific balances, rather <"than volumetric flasks">, for most things. I only use a pipette now for very small volumes 


Sammy Islam said:


> so that's why i would like to make my own solution to test.


That should tell you. You will have made <"a standard"> that you can use for calibration. 

cheers Darrel


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## Oldguy (16 Dec 2020)

Sammy Islam said:


> measuring out the water precisely.


If you have accurate scales/balance then you can weigh the water. Assume 1.00 gram per ml/cc. I have calibrated glass ware in the past working to three decimal places. B@ll breakingly tedious.

As @dw1305 says serial dilution is the best way as it reduces errors and simplifies measurements. Evan though I have 2 lire measuring cylinders I use 5litre plastic bottles and 500ml drink bottles for serial dilutions of factors of ten.

Measuring cylinders are cheap thanks to eBay should you feel the need.


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## Oldguy (16 Dec 2020)

dw1305 said:


> Just by weight.


You pipped me to the reply. I am slow at typing.


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## dw1305 (16 Dec 2020)

Hi all, 


Oldguy said:


> You pipped me to the reply. I am slow at typing.


This is <"always happening to me">, you spend ages writing a reply and then just before you post it, some-one posted the same thing. 

cheers Darrel


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## Sammy Islam (17 Dec 2020)

dw1305 said:


> Hi all,
> 
> Just by weight. Because water has a density of one,  a kilogram of water has a volume of one litre and  one gram  = one millilitre.
> 
> ...


Thanks, I have successfully made 4dkh water, i tested it a few times to make sure. I also doubled the amount of test fluid to 10ml so every drop of indicator is for 0.5dkh.  

Might test 20ml of it and increase the accuracy more, but i'm pretty happy with it. 
Might test 10ml of the ebay fluid to find out if it is 4.5 or 5dkh aswell.


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## Hanuman (29 Sep 2021)

@dw1305 Would using RO water with a TDS at ~20 be ok for making the solution or it would need to be flat 0?


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## dw1305 (29 Sep 2021)

Hi all,


Hanuman said:


> @dw1305 Would using RO water with a TDS at ~20 be ok for making the solution or it would need to be flat 0?


It depends a little bit which ions make up the twenty mg/L TDS (~60 microS), but it should be OK. It is still a <"small amount of ions">.


dw1305 said:


> If you can get pure KCl it is 0.746g KCl in one litre to give a 1411 microS solution.


Do you know how hard the water in the RO feed was? If it was slightly salty, but soft,  (for this use) it is effectively 0 ppm TDS, we are only interested in bicarbonate (HCO3) ions

Even if the TDS comprise entirely Ca++ and 2HCO3- ions it is still a small difference to the dKH (it will be <"4 and a bit" rather than "4")">.

It doesn't matter if the feed water to the RO unit had been through ion exchange (a unit that uses NaCl). It will still have <"the same carbonate content"> as the original supply.

cheers Darrel


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## Hanuman (30 Sep 2021)

dw1305 said:


> Do you know how hard the water in the RO feed was?


Raw from the faucet, the API KH test kit tells me 2.5dKH. Water from my RO unit, KH test kit tells me 0dKH. So it does seem the filter is somehow filtering carbonates or am I not understanding something? The resin filter says: "filtering limestone and calcium".
I tested the RO water TDS again today and it tells me: 17 ppm(0.7) - 12 ppm(0.5) - 26 μS


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## dw1305 (30 Sep 2021)

Hi all,


Hanuman said:


> Raw from the faucet, the API KH test kit tells me 2.5dKH. Water from my RO unit, KH test kit tells me 0dKH. So it does seem the filter is somehow filtering carbonates or am I not understanding something? The resin filter says: "filtering limestone and calcium".
> I tested the RO water TDS again today and it tells me: 17 ppm(0.7) - 12 ppm(0.5) - 26 μS


That sounds fine. There is a good explanation of <"ion exchange resins"> from Lenntech.

cheers Darrel


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## Hanuman (1 Oct 2021)

Hi Darrel,

Thank you. Should I assume the ppm in the water are mainly the Sodium ions released by the resin filter?

In any case if I read you right my RO water should be fine to prepare the dKH solution.


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## dw1305 (1 Oct 2021)

Hi all, 


Hanuman said:


> .......... Should I assume the ppm in the water are mainly the Sodium ions released by the resin filter?
> 
> In any case if I read you right my RO water should be fine to prepare the dKH solution.


The cation is likely to be sodium (Na+), the anion could be chloride (Cl-) etc.  I would have any worries about using the water to prepare your 4 dKH solution. 

cheers Darrel


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## Hanuman (1 Oct 2021)

Thank you Darrel.


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## Hanuman (4 Oct 2021)

Something just struck me. What is the need of a 4dKH solution if tank water is let's say 0dKh (at least below 0.5dKH)? Wouldn't simply using RO water at 0 dKH in the drop checker and only adding some bromo blue be more representative of the tank CO2 content? Or am I missing something?
edit: in other words matching the dkh of the tank water to the dkh of the drop checker?


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## Wookii (4 Oct 2021)

Hanuman said:


> Something just struck me. What is the need of a 4dKH solution if tank water is let's say 0dKh (at least below 0.5dKH)? Wouldn't simply using RO water at 0 dKH in the drop checker and only adding some bromo blue be more representative of the tank CO2 content? Or am I missing something?
> edit: in other words matching the dkh of the tank water to the dkh of the drop checker?



Only because most of the CO2 colour charts are created based on 30ppm CO2 in 4dKH water. If the test water is a lower KH, it will just move more towards yellow at 30ppm CO2. 

You could create your own custom chart for a lower dKH solution - though I can't imagine it would work well for 0dKH water which would probably be full yellow at very low CO2 levels - but there isn't really much point, as the difference between the KH of the tank water and test water isn't really relevant to the measurement of the dissolved CO2.

The reduction is the KH of the test solution is perhaps most useful if you have a specific dissolved CO2 target in mind. For example, if you wanted to target 15ppm CO2 instead of 30ppm, you could use 2dKH solution, and then aim for the same green colour in that as you would get with 30ppm and 4dKH solution.


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## Hanuman (4 Oct 2021)

Wookii said:


> You could create your own custom chart for a lower dKH solution - though I can't imagine it would work well for 0dKH water which would probably be full yellow at very low CO2 levels - but there isn't really much point, as the difference between the KH of the tank water and test water isn't really relevant to the measurement of the dissolved CO2.
> 
> The reduction is the KH of the test solution is perhaps most useful if you have a specific dissolved CO2 target in mind. For example, if you wanted to target 15ppm CO2 instead of 30ppm, you could use 2dKH solution, and then aim for the same green colour in that as you would get with 30ppm and 4dKH solution.


Indeed. Not sure what I was thinking. Thanks for waking me up. 

The reality is that I do not use the drop checker to quantify CO2 in my tank, instead I use the PH drop. The first and only reason I still use a drop checker is to simply make sure there is CO2 in the tank. That's it, nothing more. If I see it green or blue then I know either my CO2 bottle is empty or something funky happened with the reg or tubbing.


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