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DIY Drop Checker

273195 Views 357 Replies 80 Participants Last post by  HeyPK
It is quite easy to make your own "Drop Checker" or CO2 Indicator from acrylic sheet. The object is to have a small device that holds a few ml of water/indicator solution under the water line of the tank, so there is an air gap between the tank water and the indicator solution water. The commercial versions of this range from the elegant ADA glass unit, which is currently out of stock, to a much cheaper imitation ADA glass unit from Hong Kong, to a Red Sea plastic unit which is still cheaper. All do the same job. Two of the commercial versions are the imiitation ADA unit:

and the Red Sea unit:

Both are available on ebay at: eBay: Type2 Co2 Drop Checker-monitoring proper dosage of CO2 (item 250038130859 end time Oct-18-06 09:05:18 PDT)
and eBay: CO2 Indicator Red Sea Real Time CO2 Monitor (item 300036151186 end time Oct-14-06 09:48:10 PDT)

The easiest way to DIY this is to use all straight lines and rectangles, and make it from acrylic plastic. I made one a couple of years ago, but hadn't figured out how to effectively use it so I tossed it. Here is what it looks like:

All of the pieces of acrylic have to have squared edges, and the pieces that establish the thickness of the device should be cut from a constant width strip. When glueing these together, remember, the assembly has to be air and water tight, and any smearing of the cement makes it hard to see the color of the indicator solution. For an indicator solution you can use the solution from an Aquarium Pharmaceuticals pH test kit, or any other test kit that gives yellow at pH=6 and blue at pH=7.2 - use at least double the number of drops of indicator solution as the kit says to use, to get a more intense color. (Using even 4X the recommended number of drops doesn't change the test reading, only the intensity of the color.) To use this see:
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The sponge helped the response time a bit, but not by as much as I expected. It took 10 - 15 minutes for the color to reach about 2/3 of the way to the final color. So, I tried one last design, using the Tyvek Priority Mail envelope material:

This one used the same size KH reference sample, the same amount of indicator reagent, a sponge, but a Tyvek membrane. It reacted exactly the same as the one above using the Cole Parmer transparent membrane. This one is easy to make, a piece of plastic, an O-ring, and a suction cup airline holder. It took me about an hour to make. It is easy to load, easy to read, easy to make, and responds almost 10 times faster than the glass drop checker. And, everyone should be able to get a Priority Mail envelope to use as a membrane. I think I have exhausted all of the ways to make a drop checker!
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I like this design as I have all the supplies to do this one but I can't figure out where the reading is coming from... Is it just the sandwiched Tyvek membrane spaced from the O ring that is allowing the exchange in reading ? Or am I missing something as to where membrane is exposed to the water ?
One flat piece of acrylic has a hole in it. The membrane goes across the hole, over the O-ring, and then between the two pieces of acrylic. That leaves a disc consisting of membrane, piece of sponge soaked with KH reference water, acrylic, with the O-ring sealing in the KH reference water. I wasn't too happy with this design, and I'm not all that sure the tyvek membrane doesn't leak a bit. Personally, I am giving up the quest for faster response, preferring the simplicity of not using the membrane.
Wow! What a neat and easy way to make one of these gadgets. The only suggestion I have is to keep the quantity of water in it to a minimum to speed up the reaction time.
The real breakthrough in that shot glass design is thinking outside the box, by noting that there is no good reason to keep the two parts concentric. That suggests getting two sizes of test tubes, cutting them shorter and glueing the small diameter one inside the large diameter one as you did. Even doing the non-concentric thing when making one from acrylic tubes would be much easier. One could also experiment by making the air chamber glass much bigger than the water chamber glass, to see if that speeds up the reaction. Now I think anyone can make one of these, even the all thumbs people.
Baking soda is not an exact crystal form of a chemical compound. It can have lots of water incorporated into the structure or very, very little. And, that affects the weight of a given amount of bicarbonate. Also, sodium bicarbonate can contain some sodium carbonate, which changes the percentage of carbonate per gram. (If you heat baking soda to dry it, you also convert part of it to sodium carbonate.) So, it isn't possible to specify with great accuracy what weight of baking soda to mix with a liter of water to arrive at 4 dKH. But, if you buy a certified KH solution, whatever the KH is, you can accurately dilute it with distilled water to arrive at 4 dKH with good accuracy. That is how the 4 dKH solutions we can now buy are made.
It is very difficult to get any accuracy making 4 dKH water with baking soda. I think I would rather trust a KH test kit instead, then just slowly adjust the KH until the test kit says it is 4 dKH.
Just the pH test liquid goes in with the 4 dKH distilled water. What you are doing is measuring the pH of that bit of water, which will be about 6.6 when the color is green, and pH 6.6 plus 4 dKH equals 30 ppm of CO2.
so whats the highest KH people are using in the drop checkers and still seeing bba develop?
using a drop checker with a KH of 4 im still seeing some BBA develop on the spray bars and co2 line...
The drop checker just gives you a good estimate of how much CO2 is in the water. It does nothing itself for BBA, which I'm sure you already knew. This is a subtle hint for starting this thread in the algae forum.
There is always more to learn! Yesterday I found that the green color I was seeing for my drop checker was almost entirely a reflection of the plants color. When I pulled the little thing out of the tank, the fluid was very, very yellow! And, when I checked my CO2, I found that the tank was near empty. So, today, with a full tank I have been watching it more often - if you have enough pH reagent in it to get a strong blue color, you can easily see that it is green when it gets there. But, if you find you have to squint, move your head around, and work to see what the color is, it is very likely that it is yellow, which can be a very light color even when the fluid was very strongly blue to start with. Fortunately I didn't lose any fish this time, unlike the last time I ran out of CO2, and because I had 3 dKH water in it the actual amount of CO2 I had when it was so yellow was probably around 80-90 ppm, bad enough, but not a total disaster since I caught it pretty quickly.
I would like to throw my hat in the ring when I first read this thread I had no idea what a drop checker was now I know and have built my own thanks hoppy
You are welcome, and that is a nice looking job you did. If you now use white finger nail polish to paint the inside surface of that center tube you will have a nice white background to view the color against. Or, am I looking at it wrong? Is the fluid in the annulus or inside the small tube in the middle?
The sand paper idea didn't work well for me - the water makes the white become almost transparent. Nail polish is acrylic, the same material as the tubes, so it is the perfect "paint" for acrylic. And, that idea definitely works, if you can find white nail polish.
The solution contains a dye - the bromothymol blue dye that is the pH indicator reagent. Dyes do fade over time. Also, the drop checker will gradually accumulate biofilm and need to be cleaned thoroughly. Most people seem to be replacing the fluid and cleaning it about every two weeks.

It is intended to be left in the tank full time. If you remove it, the solution in it will start evaporating and that will make it inaccurate.
Silicone isn't the best way to glue acrylic, but if it works, it works. Let us know how this works in the aquarium. Are you going to attach a suction cup to hold it in the aquarium?
Acrylic cement is just a solvent that softens the acrylic, so it welds to another piece of acrylic. The high viscosity type cement has pieces of acrylic dissolved in the solvent, so it can also fill gaps or make filets at the corners. I use the high viscosity type. I buy it at the "Tap Plastic" store near me.
Wow! I'll bet high school chemistry labs will all be short on funnels and test tubes now. That one is an extremely easy to make variation, and good looking too.
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