# How to check your drop checker....



## ian_m (7 Nov 2016)

Almost every couple of days there is someone on this forum who reports they cannot get their drop checker to change colour despite everything they try.

In almost 100% percent of the cases it because of poor CO2 injection and distribution in the tank.

However, despite many members repeating the "you have poor CO2 injection and distribution" mantra they refuse to believe the drop checker and convince themselves that "the drop checker must be wrong, as I must have decent CO2 injection and distribution".

Well here is how to verify your drop checker works.

Below is my drop checker freshly filled with Neutro 4dKG Bromo Blue indicator. The blue indicates no CO2 in the fluid as would be expected from the sealed bottle.





Now if you turn the drop checker upside down (and try not to spill the fluid as I did ) and then breathe into it followed by a bit of shaking (of the drop checker, not you ) and repeating, you can quite easily get the fluid to turn green and even yellow. Took me a minute or two to get my drop checker this colour.




So my drop checker works.

Obviously doesn't verify that there is 30ppm CO2, but it shows at least that the drop checker fluid can be made to change colour in presence of CO2.


----------



## AverageWhiteBloke (7 Nov 2016)

I think another thing is the that there are so many other variables with DC's. I personally have three, one large standard one, a nano version of that and a hang on the side one. They all appear to react in very different ways. For instance, in order of reaction times the hang on one is the slowest, followed by the Nano then the large one being the quickest. It would appear that the more surface area exposed the quicker the DC is to react. Maybe just an assumption on my part but it does for me time and time again.
Another issue I find is with the 4DKH/Bromo pre-mixed fluids. I don't think I've come across one yet that was visibly clear inside of a lit aquarium. The colour is just so weak in them they are nigh on transparent. I tend to use the pre-mixed stuff just in the hang on DC where you can get a better reading outside of the tank but as I say it is very slow to react. The one in the tank I tend to mix my own with a couple of extra drops of bromo but then you start asking yourself at what point is a couple of extra drops too many. Being only a couple of mil of 4DKH it doesn't take too many extra drops before you've diluted it down to possibly only having a 3dkh fluid I guess.
The last WC I did I put both fresh hang on and a normal DC in the tank together in roughly the same place. The one in the tank started reacting within about half an hour, the hangon took a couple of hours! There is also the issue especially with the inline atomisers where the minute bubble are rising directly up into the DC so I guess it's not exact science by any means. We're always told it's just a guide and essentially it is. I just use mine as a quick ref as I walk past to make sure everything's within reason. I also base that on which DC I'm looking at knowing how they react differently.
Good Idea on testing them though, not sure about people putting them in their mouths though  is bromo toxic? Not sure. Maybe folk should just hold the outlet of their co2 pipe into one if they want to prove if it's working.


----------



## ian_m (8 Nov 2016)

I have been through many glass drop checkers both cheap and expensive. All of which I have ended up breaking during cleaning, dropping or even attaching to the tank.

With all of the glass ones I had difficulty reading accurately against the tank background. I used to keep a white piece of plastic handy, to poke in the tank behind the drop checker so I could easily see its colour.

However since moving to the JBL one...brilliant. Its plastic so if dropped doesn't break and it has a white piece of plastic inside which makes reading the colour in the tank easy, no faffing with white plastic sheets. Easy to clean as well, pull apart wash in sink and easily push back together.


----------



## AverageWhiteBloke (8 Nov 2016)

I agree, although not as visually pleasing better results can be obtained with any of the plastic DC's available. I have used the Dennerle one in the past, I think the fluval one is quite good. I had a white plastic ruler in my cabinet for the same reason as your white sheet to use as a back ground. Plants and lighting have a lot of impact on the perceived colour. I pulled out my DC the other night at the end of the co2 on period prior to changing some water and in the tank it looked a nice lime green, outside it was the colour of lager.


----------



## rebel (8 Nov 2016)

I wonder whether any manufacturer will make a drop checker with a tiny LED built in.... That might help visualise the colour.


----------



## doylecolmdoyle (26 Jun 2017)

This post isnt fully on topic but I have read you can add PH reagent to your drop checker indictor to make the colour darker, would this "ph reagent" just be your standard ph test fluid? I have some drop checker indicator fluid that is so clear its hard to tell the colour.

EDIT think i answered my own question, some of the cheap glass drop checkers I ordered from ebay came with bromothymol blue, I added 2 drops of the bromothymol blue to the CO2 Drop Checker Solution which was advertised as "pre-made 4dKH solution containing the appropriate amount of indicator. Easy to use, no mixing required. Simply open cap and fill CO2 checker"

It was way to clear and hard to tell the colour, but with the extra bromothymol blue it is now nice and dark and easy to tell the colour.


----------



## kadoxu (27 Jun 2017)

doylecolmdoyle said:


> EDIT think i answered my own question, some of the cheap glass drop checkers I ordered from ebay came with bromothymol blue, I added 2 drops of the bromothymol blue to the CO2 Drop Checker Solution which was advertised as "pre-made 4dKH solution containing the appropriate amount of indicator. Easy to use, no mixing required. Simply open cap and fill CO2 checker"
> 
> It was way to clear and hard to tell the colour, but with the extra bromothymol blue it is now nice and dark and easy to tell the colour.


Yes, bromothymol blue is usually used to test PH. The pre-mixed Drop Check liquid is a mix of water with a KH of 4 with bromothymol blue. The drop checker changes color because the solution's PH changes (lower PH - green/yellow, higher PH blue), just like it does when you are using a PH test kit.

With this said, I'm not sure, but I think that adding more bromothymol blue to the solution changes the way it reacts to PH changes (like testing PH using more drops than what is advised).


----------



## ian_m (27 Jun 2017)

kadoxu said:


> With this said, I'm not sure, but I think that adding more bromothymol blue to the solution changes the way it reacts to PH changes (like testing PH using more drops than what is advised).


Yes it does to a certain extent, as bromothymol blue is itself a weak acid. If adding more indicator affects the reading, I am not sure.

Someone with a pH meter needs to measure the pH of premixed indicator solution then add some more indicator and see if the pH changes.


----------



## doylecolmdoyle (27 Jun 2017)

Cheers for the feedback guys, I do have ph pen but to test would need to mix up a larger amount of indicator fluid. When I added the two extra drops of bromothymol blue the checker fluid when from a very clear green to a much darker green but generally still the same colour (but less clear)


----------



## AverageWhiteBloke (27 Jun 2017)

There's also the problem of watering down. Because we use such a small amount of 4dkh fluid in our dc's unless the bromo is also 4dkh then each drop will either soften or harden the solution I guess. Probably why pre-mixed from suppliers is so transparent, the more bromo they add the less accurate the 4dkh solution. 

Sent from my STH100-2 using Tapatalk


----------



## doylecolmdoyle (27 Jun 2017)

I only use the drop checker as a quick visual indicator that I have co2 in my tank water, not as a precise measurement of co2 as that is very subjective when it comes to shade of green/yellow, basically I just want a quick visual indicator that I have a safe level of co2 in the tank, if its so clear I cant actually tell its useless.


----------



## AverageWhiteBloke (27 Jun 2017)

Yeah, not exact science at all. As you say I just glance at mine when passing to make sure it's not too high and checking co2 is actually on without looking in the cabinet (hard to tell using an inline atomiser when lights off) I sort of get a feel for the colour in my own particular tank. The fish are more of an indicator and get lethargic when too high so even if my DC isn't bordering on yellow but the fish don't look comfortable I don't try and increase just because the DC says so. I suspect most tanks will get away with being light green in most cases, the plants and algae tell you too low the fish too high. 

Although not as aesthetically pleasing you will get a better reading off the white plastic DC's rather than the glass ones. I still add an extra drop or two to mine so I can see it clearer and just accept it is probably giving me a slightly higher reading than actual.


----------



## doylecolmdoyle (27 Jun 2017)

Very true, I have just filled another glass drop checker with just premixed 4dkh soliton and put it on the rim next to the check with the extra drops of bromo, just to compare tomorrow!


----------



## AverageWhiteBloke (27 Jun 2017)

Interested in seeing how this compares. 

Sent from my STH100-2 using Tapatalk


----------



## ian_m (27 Jun 2017)

You want this...





and not this...ooops.


----------



## doylecolmdoyle (28 Jun 2017)

AverageWhiteBloke said:


> Interested in seeing how this compares.
> 
> Sent from my STH100-2 using Tapatalk



Here are some photos from tonight, the lighter fluid is from co2art and the darker fluid is the same fluid but with one extra drop of bromothymol blue, both have been on my 1ft cube for over 24 hours, as you can see on the tank photo you cant really tell what colour the standard fluid is, at least being a bit darker its easier to tell.


----------



## AverageWhiteBloke (28 Jun 2017)

Interesting. Just shows the difference 1drop makes, looking at both of them together the one without the extra drop appears in my eyes to not only be nearly transparent but slightly bluer maybe? I use co2 art fluid as it comes in my hang on dc but the wall behind is white so I can get a reading. It's not just co2 art BTW, I have had premixed from a couple of suppliers and they all appear to be too transparent to get a reading off. Got one free with a glass diffuser once from China and I don't know what was in the bottle but it just didn't work at all. The fluid in the bottle turned yellow by itself over time.


----------



## AverageWhiteBloke (28 Jun 2017)

Here's why we shouldn't take DC colour as being a definitive answer to correct co2 levels and just a rough guide favouring how the plants are reacting. Below I've merged the images, now in my eyes you have two DC's with slightly different fluids in but kept in nigh on the same position in the aquarium. Using @ian_m DC as a comparison I would say the one on the left is more like Ian's good values and the one on the right is more like Ian's too high values. This is the fundamental floor with all visual test kits, depending on the surrounding lighting as well as other factors like the person reading the solution's mood we all interpret the results differently. Test kits like beauty are in the eye of the beholder


----------



## AverageWhiteBloke (28 Jun 2017)

I didn't actually realise that Bromo Blue was slightly acidic, one would assume that anything that measures PH should be neutral. Every day's a school day in this forum  I would say when judging co2 levels using those types of dc's you would have to factor in firstly if you add a bit more bromo it's probably measuring a touch high and because of the hang-on-side nature that they are going to be in the upper most co2 rich area of the water column so again would be measuring slightly high. These type of DC's because of this and the fact that there is little surface area of fluid exposed to gas are probably the least accurate and you could probably run a bit higher/yellower.

I have three types in my aquarium, obviously not all the time I have a hang on but it has a bulb at the end and a standard glass bulb type but I have put them all together as you have just to compare them. The results were at some point they all give pretty much the same reading however the large bulb one reacted quickest followed by the nano version of the bulbed version and finally the hang on type. It would appear the more surface area exposed to gas the quicker the fluid will react. With a caveat, because the largest of the bulb type dc's has a wider opening it meant when using an inline diffuser that more of the tiny bubbles of co2 could pop under the opening putting more co2 direct into the DC. At least the bulb types can be put in a position where you want to check co2 levels.

To say it's not exact science is probably an understatement. PH probes suffer from out of calibration as well as taking into account acids already in the tank isn't much better of an option either. So unless someone invents some other way we're stuck with the tools we have for now. I tend to have mine in a position where I suspect co2 will be at its worst, run for a few weeks and if my plants are growing and no signs of co2 related issues I note the colour of the DC and try and keep it about there. I try turning up the gas now and again and watch for the fishes reaction, first sign of discomfort I turn it back slightly. I could never get the famous 1 drop ph unit or a yellow dc in my tank. The fish just aren't having that at all but then again my tank is a planted community fish tank rather than a show stopper at the IAPL so I live with that.

Considering co2 is a moving target anyway depending on plant mass and surface agitation as well as state of filter there never will be a one-size-fits all level I guess. I can get mine as accurate as I can but following a good clip out I get higher readings, when it's due a good clip out I get lower readings. You can't keep adjusting for these circumstances, that's when BBA starts so I get a good mean average and manipulate the plants to the co2 rather than the other way round. If my readings are getting low I clip out faster growing stems and big leaves of amazons and balansae to bring things back under control. If they are high I tend to not fill my tank up to the brim as much and let some surface agitation gas a little bit off.

The co2 fight continues...


----------



## AverageWhiteBloke (28 Jun 2017)

Just to add... I think a better solution would be a combination of the two I.E, a ph probe inside of a glass bulb that contained a 4dkh solution. My money is waiting for that invention, dragons den anybody?  Maybe we should get UKAPS members to crowd fund it.


----------



## doylecolmdoyle (29 Jun 2017)

True that the co2 art fluid does give a better reading when used against a white background and probably doesn't need the extra bromo when used in that situation. I also use a PH pen to keep a eye on how much ph drop I am getting, still hard to say it collaborated 100% accurately.


----------



## X3NiTH (29 Jun 2017)

And to confuse matters even more there are actually two types of bromothymol blue. Protonated and De-protonated.

De-protonated appears as a blue liquid before adding to ?dKH water.

Protonated appears as a red liquid before adding to ?dKH water. (Looks red in the bottle but is actually concentrated yellow and stains yellow on a blot test).

I put ?KH above because they act the same way no matter the KH of the stock solution water. I have done side by side tests using the same KH of water, the standard 4dKH and my tank dKH which at the time was dKH9. The water I used at 9dKH was my water change water before adding GH salts, it is reconstituted RO/DI using KHCO3 at 8.1g per 25L, the reason for doing this is that according to the ph/KH/CO₂ chart the curve is quite flat here and so the colour change is more gradual and more accurate than a lower KH which indicates in a narrower window.

I found that regardless of the dKH of the stock water solution Protonated Bromothymol blue will indicate 30ppm CO₂ well before the De-Protonated does if the advice you are following is a green drop checker meaning 30ppm CO₂. If this is the advice you are following then with Protonated indicator you will be underdosing CO₂. If you go by a yellow dropchecker for 30ppm CO₂ using De-Protonated indicator for 30ppm then you're overdosing CO₂.

If using Protonated Bromothymol Blue you want a yellow dropchecker for 30ppm.

If using De-Protonated Bromothymol Blue you want a green dropchecker for 30ppm.






Both the dropcheckers on the left were photographed immediately after removing them from the tank, the checker on the right is a control which never went in the tank and is the colour for atmosphere equilibrium (both liquids indicate this colour for atmosphere equilibrium when added to whatever dKH water). Dosage for the indicators was at 3 drops per 5ml of dKH water, this test pic was 4dKH stock solution. The differing size of the dropchekers above made no difference when compared to a later test using both same sized dropchekers (not photographed), the reaction was the same.

Using a lower concentration of indicator say one drop per 5ml narrows the inaccuracy window but makes it very hard to read.


----------



## doylecolmdoyle (30 Jun 2017)

X3NiTH said:


> And to confuse matters even more there are actually two types of bromothymol blue. Protonated and De-protonated.
> 
> De-protonated appears as a blue liquid before adding to ?dKH water.
> 
> ...



Interesting! Thanks for that post, the Bromothymol blue I had been adding to the co2art pre mixed checker fluid was the red Protonated but I have no idea what Bromothymol blue they originally mixed to make the solution, I should really make up my own dKH water then add the red Protonated Bromothymol blue, reading your post above am I understanding this correctly... you are saying it doesn't matter what dKH of the stock water solution is? So I could just use distilled water in my checker then add the red Protonated Bromothymol blue rather then trying to create 4dKH water?


----------



## AverageWhiteBloke (30 Jun 2017)

Don't think that would work. Distilled water tends to absorb co2 from the atmosphere and will probably go yellow out of the tank. 

Sent from my STH100-2 using Tapatalk


----------



## ian_m (30 Jun 2017)

AverageWhiteBloke said:


> Don't think that would work. Distilled water tends to absorb co2 from the atmosphere and will probably go yellow out of the tank


Yes distilled water will take up CO2 from atmosphere but only until in equilibrium with the 400ppm present in air. You use Henry's law (I thinks that the one) to work out the ppm in water based on partial pressures, which if I remember correctly give 0.6ppm. 0.6ppm won't have any effect on your indicator.


----------



## dw1305 (30 Jun 2017)

Hi all,





AverageWhiteBloke said:


> I didn't actually realise that Bromo Blue was slightly acidic, one would assume that anything that measures PH should be neutral.


You can ignore the acid bit. 

If you make it up from scratch you start with the sodium salt of bromothymol blue, and you add a very small amount to DI water, (it is something like 0.5g of the salt made up to one litre), and that makes a really dark blue solution. 

I assume this is because sodium (Na) is an alkali metal, so the sodium bromothymol blue solution is blue. Presumably by the time you've added a couple of drops of indicator to the 4dKH solution it really doesn't make any difference to the pH.





X3NiTH said:


> De-protonated appears as a blue liquid before adding to ?dKH water. Protonated appears as a red liquid before adding to ?dKH water. (Looks red in the bottle but is actually concentrated yellow and stains yellow on a blot test).


I think the protonated - deprotonated bit is actually the pH change. 

Deprotonated is at a pH above pH7.6 (conjugated base), and the indicator is blue, when you add an acid (defined as a "proton donor") in solution the indicator becomes protonated (it has accepted a proton)  and the color changes to yellow (conjugated acid). 

In the bottle it is a concentrated solution of the conjugated (protonated) acid  and appears darker and more red (just like yellow food dye)). I assume if you start with bromothymol blue (not the sodium salt) you end up with the protonated yellow solution, via the dissolution of CO2 (but it is still a weak acid). 

When you are at ~pH7 you have a mixture of protonated (yellow) acid and deprotonated (blue) base, and yellow and blue make green. 

There is an explanation (with the chemistry) at <"The acidic form of .....">.

cheers Darrel


----------



## AverageWhiteBloke (30 Jun 2017)

ian_m said:


> Yes distilled water will take up CO2 from atmosphere but only until in equilibrium with the 400ppm present in air. You use Henry's law (I thinks that the one) to work out the ppm in water based on partial pressures, which if I remember correctly give 0.6ppm. 0.6ppm won't have any effect on your indicator.



OK, back back in the day before stumbling across this board and before much info was available I use an API de-ioniser resin and thought it would be a good idea to use de-ion water in the DC as I had heard about tank water affecting the measure. The fluid pretty much turned yellow although thinking about it that was probably because I was injecting co2 and it wouldn't take much to turn yellow I guess with de-io water. I think I also tested my WC water after de-ionising it before going in the tank for PH and that was also very acidic.


----------



## jaypeecee (27 Dec 2018)

ian_m said:


> However since moving to the JBL one...brilliant. Its plastic so if dropped doesn't break and it has a white piece of plastic inside which makes reading the colour in the tank easy, no faffing with white plastic sheets. Easy to clean as well, pull apart wash in sink and easily push back together.



A problem with the JBL DC is that, if a film of organic (or any other) material develops at its interface with the tank water, it can't be seen. And that can lead to misleading CO2 indication. That's a problem that I had with the JBL DC that I own. The 'white' piece of plastic also discolours over time.


----------



## jaypeecee (27 Dec 2018)

X3NiTH said:


> The water I used at 9dKH was my water change water before adding GH salts, it is reconstituted RO/DI using KHCO3 at 8.1g per 25L...



Hi X3NiTH,

I don't have access to potassium bicarbonate. Would sodium bicarbonate be OK? And, if I understand you rightly, does this result in 9dKH?

JPC


----------



## AverageWhiteBloke (27 Dec 2018)

What is it you're trying to do Jay?


----------



## jaypeecee (27 Dec 2018)

AverageWhiteBloke said:


> What is it you're trying to do Jay?



I currently make up my DC solution to 4dKH using sodium bicarbonate, which works well. But I was interested in X3NiTH's reference to KHCO3, i.e. potassium bicarbonate.


----------



## AverageWhiteBloke (27 Dec 2018)

Ahh ok mate. To be fair I think the only important bit is the "bi-carbonate" as long as the solution is 4KH doesn't really matter. They sell potassium bicarbonate on ebay, I get some for raising my very soft tank water. 4KH solutions are so cheap though so hardly worth diy'ng them I find. Are you having some problems with yours or something?


----------



## X3NiTH (28 Dec 2018)

I used Potassium Bicarbonate in the drop checker mainly because I had it but also because the plants would enjoy the extra potassium more if the drop checker accidentally fell from the tank wall and disgorged its contents into the water column (yeah I've done that before).


----------



## Craig Matthews (7 Jan 2019)

I have a question if you don't mind please, my jbl permanent drop checker co2 plus test kit....
https://www.pro-shrimp.co.uk/water-...weIM_Gu3lkCWA58yT2-4tMy9RJlxZEMIaAu7AEALw_wcB
Is a fluid that doesn't require mixing with tank water etc... Just 35 drops in the checker.it says takes upto 2 hrs to change colour so I have my co2 come on 2hrs before lights on and co2 is running for 8 hrs and photoperiod which is 7 hrs long. After 2 hrs the checker is still blue, after 3 hrs it's changing to green and by 4 hrs is pretty much moss green. 5 hrs it's changing to lime green and 6 hrs until co2 off its consistently lime green. How soon should it be lime green? If I up the co2 to get it lime sooner then by 6hrs of injection I'll be over shooting. Thanks in advance.


----------



## ian_m (8 Jan 2019)

Have you verified your drop checker works, by doing the breath test as in the first post in this thread ? Just to verify the indicator solution is working.

See this thread for the maths of how CO2 concentration varies with time.
https://www.ukaps.org/forum/threads/co2-concentration-versus-time-the-maths.51423/

So to get drop checker green at lights on..

- You need to increase your in injection rate as well as increase surface agitation. Injection rate roughly controls how quickly its gets to green and surface agitation increases loss rate which limits the maximum CO2.

- Leave injection rate the same, but decrease the loss due surface agitation and/or cr*p CO2 injection method.

You haven't told us your tank size and CO2 injection method.

I had great difficulty getting green drop checker (all over then tank) at lights on using an in tank diffuser, but as soon as I switched to inline diffuser and didn't change injection rate BANG yellow drop checker, fish gasping...oops.

It will take a while to get injection rate, CO2 loss rate adjusted so that drop checker is nicely green at lights on.


----------



## Craig Matthews (8 Jan 2019)

It's a 70 litre tank quite heavily planted with the fluval u3 filter I use the integrated spray bar for under water flow. The glass ceramic diffuser is situated at the outflow and blown about the aquarium. Drop checker works as it changes colour throughout the injection period and Sunday I refilled with new fluid. I'm already on 2 bps and it's only 70 litre


----------



## ian_m (8 Jan 2019)

Ceramic glass diffuser wont help, not the most efficient was of injecting CO2.

Try increasing the CO2 rate and angling the spray bar upwards a bit.


----------



## Craig Matthews (8 Jan 2019)

Ok I'll give it ago cheers,


----------

