# DIY CO2 Drop Checker



## Darkblade48

Many people these days are trying their hand at planted tanks, and as such, sometimes CO2 injection becomes a necessity due to the high light they have. So, here's an invaluable piece of equipment that can be used to estimate the amount of CO2 in your aquarium.

Here's the equipment you will need, or rather, the stuff that I had lying around my house that I used:

1 Glass container with screw on lid
1 Silicon glue applicator/similar type glue applicator
1 Rubber O ring that is about the same size as the screw on lid
Power drill with appropriate drill bits
1 Suction cup
1 Zip tie

Pictures!

Glass container with lid


Glue applicator with the tip cut off so it will fit into the glass container


O Ring

As mentioned, you'll have to cut the plastic applicator so that it fits within your container first. Next, you'll want to drill a hole in the cap.


Finally, you can put the O-ring onto the applicator, put the applicator in, and screw on the lid.

Next, I needed some way to mount the whole thing in my nano, so I used a spare suction cup and a plastic zip tie.


You'll notice the zip tie just goes through the suction cup (i.e. I just put a hole through the nipple of the suction cup).

After the mechanical work was done, I had to start the chemistry part (I love chemistry!)

Items you'll need to make a 4 dkH reference solution for the drop checker:

1 Graduated Cylinder
1 Scale that can measure to at least 0.1 gram accuracy
1 Box of Baking Soda
1 Bottle of Distilled water

Pictures!

Scale that I bought off a site, it was $11 (free shipping)


Baking soda (sodium bicarbonate), you can pick this up at your grocery store.


Distilled water, again, grocery store.

First, since a 4 dkH reference solution is needed, I made the necessary calculations and prepared a 40 dkH solution before diluting it 10 fold to 4 dkH.

To make a 40 dkH solution, you need 1.2 grams of baking soda per 1 L of water. I made up a 2 L batch, so I needed 2.4 grams (the bigger the batch, the more accurate your final solution will become).

Then, taking 50 mL of the 40 dkH solution (measured with a graduated cylinder), I poured it into a bottle and filled the last 450 mL with distilled water (giving me a 1:10 dilution = 4 dkH solution).

After you make your 4 dkH solution, measure out 5 mL, and using a pH test kit (i.e. I used the API pH test kit, any test kit that uses bromothymol blue will be fine for this purpose), put in at least double the recommended number of drops (i.e. API recommends 6, I put in 8-9 drops). This makes the resulting solution darker, and easier to read.


Here's the liquid inside the drop checker.


Everything put together, just awaiting me to strap the drop checker to the suction cup.


The whole contraption has been placed into my nano, around 4:48 pm. At the time of writing this up (5:35 pm) the top portion of the liquid is already starting to turn green. 


6:28 pm now, it's definitely green


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## blossom112

I have the Co2 indicator drops , so I will use this instead of the API ph drops ...
so I would put as many drops in as it takes to get dark blue ..

I am going to try and make some 4dkh .. following your instructions .
now instead of buying distilled can I just boil water ....
I could try both .
how do you test the water to be sure it is 4dkh after I have completed ,just set with indicator and wait ?

Wish me luck!!!


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## Darkblade48

blossom112 said:


> I have the Co2 indicator drops , so I will use this instead of the API ph drops ...
> so I would put as many drops in as it takes to get dark blue ..


The "indicator drops" is simply bromothymol blue. The API pH test kit (normal pH) is this exact chemical, so it will work for this purpose.



blossom112 said:


> I am going to try and make some 4dkh .. following your instructions .
> now instead of buying distilled can I just boil water ....


No, you should use distilled water. It'll save you the hassle of trying to obtain your own distilled water (and you'll also avoid any unknowns - i.e. how do you know exactly how pure your distilled water is, etc).



blossom112 said:


> how do you test the water to be sure it is 4dkh after I have completed ,just set with indicator and wait ?


You should use a kH test kit in order to check if your reference solution is 4 dkH or not. Do note that if you double the volume of the water (i.e. if the kit recommends 5 mL, but you use 10 mL to test), then the accuracy of your kit is effectively doubled (i.e. it can now read to 0.5 dkH instead of to the nearest whole number). Alternatively, you could (say) quadruple the volume of water, and you will get a kH resolution down to 0.25 dkH.


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## blossom112

my API ph test is for saltwater and isnt blue ? its redish brown ...
is the freshwater one different ?
Looks like I cant try this weekend we have to find a way to measure exact grams ...I thaught hubby had something in his million boxes lol 

I would really love a lesson from you once we get sorted out and painted here .
I find myself reading your pages over and over again so I can remember everything and it is all very interesting .....makes saltwater a walk in the park .
next year I will be like this is so easy lol
what is the best freshwater kit to buy ? Ill pick one up tomorrow.


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## Darkblade48

blossom112 said:


> my API ph test is for saltwater and isnt blue ? its redish brown ...
> is the freshwater one different ?


If that's the case, then the saltwater and freshwater pH test kits are different. You will have to use bromothymol blue, which is found in the freshwater API pH test kit.



blossom112 said:


> Looks like I cant try this weekend we have to find a way to measure exact grams ...I thaught hubby had something in his million boxes lol


You could always pick up a relatively cheap scale off eBay or the like. It's not the best, but for our purposes, it'll work.



blossom112 said:


> I would really love a lesson from you once we get sorted out and painted here .
> what is the best freshwater kit to buy ? Ill pick one up tomorrow.


I'm glad to be of help; I'll try to help as much as I can. As for the "best" freshwater test kit, I'm using the API test kits, and it's worked fine for me so far. Of course, if you feel like spending lots of money, you could get LaMotte test kits, but that's overkill for the aquarium hobby


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## _Green_

Thanks for posting this tutorial, you instructions are very easy to follow. 

What site did you get the same from? I need to get one and $11 and free shipping seems like a great deal.

I went to the dollar store today but was unable to find anything like what you have. I'm thinking a hobby shop or craft store might be a good place to find something. Where did you get the bottle/jar that you used?

Thanks
Ross


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## Darkblade48

_Green_ said:


> What site did you get the same from? I need to get one and $11 and free shipping seems like a great deal.


I sent you a PM with the link to the site. Do be aware that scales of this price will be prone to "creeping digit syndrome" (i.e. repeated weighings of the same object will sometimes have slowly increasing weights, i.e. 10.00 grams, 10.01, 10.02, etc). However, for our purposes, these scales work fine.



_Green_ said:


> I went to the dollar store today but was unable to find anything like what you have. I'm thinking a hobby shop or craft store might be a good place to find something. Where did you get the bottle/jar that you used?


I found my bottles at Active Surplus (it's downtown on Queen Street and St. George/Beverly). They have a pretty high stock turnaround, so you might want to check back frequently if they don't have it one week.


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## _Green_

Darkblade48 said:


> I sent you a PM with the link to the site. Do be aware that scales of this price will be prone to "creeping digit syndrome" (i.e. repeated weighings of the same object will sometimes have slowly increasing weights, i.e. 10.00 grams, 10.01, 10.02, etc). However, for our purposes, these scales work fine.


Thanks for the heads up, but as you said for the price I won't complain.



Darkblade48 said:


> found my bottles at Active Surplus (it's downtown on Queen Street and St. George/Beverly). They have a pretty high stock turnaround, so you might want to check back frequently if they don't have it one week.


That's pretty far for me, so I think I'll try to find something closer to home.

Ross


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## shrtmann

So just wondering what i can do with the remaining 1950ml of 40 dhk solution....is it safe to just add it to my tank??? or can i thirow it in my 5g jug of distilled water...im assuming it would be almost non measurable when diluted with this much water....

seems like a waste to throw away and i just water'd all my house plants yesterday so thats out of the question


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## Darkblade48

It depends how large your tank is 

I would just store the 40 dkH reference solution. Since I have access to lab equipment, I usually make much smaller (and much more accurate and reliable) batches nowadays too.


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## shrtmann

well i have a 75g tank..so im assuming itd do almost nothing at all...

i just dumped it into the 5g jug of distilled water....and saved the big batch of 4dkh solution in an old apple juice jug as my drop checker takes like 1-5 mL so itd take me forever to use what i have now....oh and my drop checker is a nice green colour..i think i may use more solution next time to give it more colour...

how often are you supposed to change the solution in your drop checker? Monthly?


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## Darkblade48

It's always a good idea to save a bunch, just in case you need to remake it. It should store relatively well, as long as you don't let it evaporate. 

You can always add more bromothymol blue to your drop checker, if you feel the colouration is too pale. I personally add anywhere from 6-8 drops so I can see the green colour. Some people like to add more, some less.

As for the drop checker solution, some people insist on changing it everytime they do a water change, others just leave it alone. 

I've left the drop checker solutions for months at a time, with no apparent ill effect *shrug*


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