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CO2 Drop Checker

11K views 17 replies 9 participants last post by  theatermusic87 
#1 ·
A "drop checker", the name ADA first called it, is a useful, cheap way to monitor the CO2 level in a planted tank. It is not a scientific instrument, because it gives only a rough estimate of the CO2 level, and it reacts to changes in CO2 level pretty slowly, typically taking 2 hours to read "correctly". But, it is cheap, easy to use, and useful.

We have been using 4 dKH water in our drop checkers for about the past 10 years, because, with that KH, the water becomes green at about 30 ppm of CO2. 30 ppm of CO2 was considered to be the optimum for getting the effect of CO2 on our plants. That was never the real optimum CO2 level except when using specific light intensity, with average oxygenation of the water, with average fish, etc. Many advanced hobbyists have been using much higher CO2 levels with their high light tanks.

It is now known that, for low to low-medium light tanks, we gain very little by having our CO2 level as high as 30 ppm. Most of the benefit from using CO2, for low to low-medium light tanks comes with about 10 ppm or less CO2. This makes using 4 dKH water in our drop checkers a poor choice.

This chart shows the drop checker colors we get with various KH water, for various ppm of CO2.



You can see that using 4 dKH water makes a drop checker useless if your goal is to have 5-10 ppm of CO2 in the water. But, 0.5 dKH water works very well.

Fortunately it is easy to make 0.5 dKH water from 4 dKH water. All you have to do is buy a gallon of distilled water at the local big grocery store. Then mix 1 part of 4 dKH water with 7 parts distilled water. You can measure water in liquid ounces with acceptable accuracy, so mix one ounce of 4 dKH water with 7 ounces of distilled water, and you now have 8 ounces of 0.5 dKH water.

I have been using this for a 2-3 weeks now, and find it to be very interesting! You can actually see the effect of the plants consuming the CO2 in the tank water (when you are not supplying any CO2) - the drop checker fluid becomes much more blue. Then, after a 16 hour lights-off period, the drop checker fluid goes back to a yellowish green. And, adding just a bubble per second of DIY CO2 in a 65 gallon tank keeps the color in the yellowish green area.

Don't look at this as increased complexity, but as a new, interesting low maintenance toy in the tank!
 
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#5 ·
that's a pretty neat chart, wonder what it'd show on a non co2 injected tank fright before lights on and during a siesta period
The time lag as the drop checker reaches equilibrium with the tank water is long enough that you might not get much change in color if your siesta was only 2 hours. But, if it was 4 hours, and you had 0.5 dKH water, you would see the color move from green, well into the lights on period to a yellow tinted green after the lights go off. That's what I saw with mine.
 
#9 ·
I've got myself some diy drop checkers going, just set them up, using some 1dkh water and ph low as indicator solution (I read somewhere that that would work as a solution)

It is a mini spring clamp holding a mini tic tac container with an api test tube inside... took all of about 30 seconds to put together (hardest part was getting distilled water and making 1 dkh water)

A quick picture to show it off
 

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#17 ·
Well I tried this method of drop checker for a couple months, and thought since I never saw a change in color of the solution, that I either had too much indicator solution, or not enough co2 to register a result; so I took them off all 3 of the tanks. I stumbled across a thread over thanksgiving that piqued my interest in experimenting; cause who doesn't like booze as a bi-product! Anyways I set up a couple bottles and thought... hmm let me check and see if I'm getting anymore co2, so out came the "drop checkers" and i tested the fluid with the breathe into an airline and bubble the liquid to see if it changed color (which it did so the diy solution works), however, i put the drop checkers in a week ago, and the drop checkers haven't changed color back towards no co2. I know that I'm not putting nearly that much co2 into the tank (regular ph test shows maybe at best a 0.2 ph drop) so my thinking is my diy drop checkers don't have enough surface area for the volume of fluid that's in the test tube. I'm going to empty some of the fluid and see if that changes anything; and if not, I'm going to possibly look into another diy option, or consider purchasing a couple of commercially made drop checkers to continue my experiment.
 
#10 ·
Excellent Chart Hoppy! For my particular tank I have been thinking 15-20ppm would be a MUCH better sweet spot than 30ppm. My biggest problem was figuring out how to correctly make the drop checker show that. Now with this thread I have a much better idea on how to do what I want. Again, thank you!
 
#11 ·
I'm in on this,got 2 new DC's coming.
Comes with brom blue & 4dKH solution.
plan is to run 1 @ 4k & the other with my seasoned Tap water which is ~1 or less
new TDS meter says seasoned tap is 35ppm.
if tap doesnt respond well then I'll dilute 5ml of 4k into a 20ml solution & test that (result would be 1k),then go from there Not using any Co2,excel when i remb.
dilution calc here for who needs 1 does it all mg,ml,mols etc.
Dilution Calculator -- EndMemo
 
#13 ·
I'm in on this,got 2 new DC's coming.
Comes with brom blue & 4dKH solution.
plan is to run 1 @ 4k & the other with my seasoned Tap water which is ~1 or less
new TDS meter says seasoned tap is 35ppm.
if tap doesnt respond well then I'll dilute 5ml of 4k into a 20ml solution & test that (result would be 1k),then go from there Not using any Co2,excel when i remb.
dilution calc here for who needs 1 does it all mg,ml,mols etc.
Dilution Calculator -- EndMemo
I am a bit confused - what is the point of using a drop checker with tap water? Unless the only contributer to carbonate hardness is carbonate and bicarbonate, the pH/kH/CO2 relationship cannot be used. It is unlikely this is the case with your tap water.

Additionally, if you are not injecting CO2 and are only using Excel, the drop checker will not give you any meaningful data.
 
#15 ·
Very good timing and just right info for me at this time. I have a 120 that I came so close to gassing that I now have no CO2 on that tank! I've been working toward doing what plants will work for that tanks as the fish are my main concern. This will give me a way to get some idea of the low to very low level I will be willing to add.
As a side issue, I have wondered if we could not improve the function of the drop checker with a better design. Many seem to have a very limited water/air exposure where the action takes place to change the color. Does anybody have some thoughts on using a much larger surface area exposed? Would a larger exposed area change the color more rapidly, making it follow closer? If not, I will give it a try at some point as I DIY my drop checker who I do use them so making a larger might just be easier in some ways.
Obvious it is not for lots of tanks due to the unsightly nature but it might also make it really much easier to define the color on a four inch long strip than a one inch!
 
#16 ·
http://www.plantedtank.net/forums/20-diy/131565-making-fast-response-drop-checker.html This is the last drop checker design I came up with. It is a fast response device, at least twice as fast as the standard ones. It is easy to make. The only problem I had with them was the short life of the solutions in the little trays. There is such a small amount it can easily be contaminated or spilled. The last thing I did with this design was try to make a mold of it and cast it from epoxy. That never did work out.
 
#18 ·
Though I would update again, since changing the amount of solution in my "drop checker" made a huge difference. Now they are changing color over the course of about and hour or so. I put solution in the test tube that had been shaken vigorously to get it "acclimated" to the amount of co2 in the air, and it was a nice DARK blue, came back after it had been in the tank for an hour and it was a nice light green


Thats the tank with the diy yeast co2 going on it (25g), at about 0.5-1 bps


This is my 5g tank with no additional co2 added, and minimal surface agitation, with the atmosphere color next to it for comparison


both of these pictures were taken mid photo period, with 1dkh solution. I'm figuring that both tanks have roughly 5ppm of co2 disolved in them atm. I'll be checking them again in the morning before lights on and seeing if there is much of a difference
 
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