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DIY Drop Checker

273189 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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Another way to weld the plastic bottle is to use a cheap soldering iron, the lower the wattage the better. Then you can use the extra bottle material cut in strips for welding rod to fill in the gaps.

I have used a variac to control the heat of the soldering iron. you may be able to use a dimmer to turn it down a bit also.
When I moved last year and got rid of my workshop tools I apparently also got rid of my soldering gun and iron. In any case I couldn't find them. I suspect that they would be much too hot for PET plastic - there seems to be a narrow temperature band when the stuff welds and doesn't char. Don't even the cheap soldering irons have a temperature control of some kind built in? If so, how would dropping the voltage affect the temperature?

The DIY drop checker was still working this morning, with no leaks that I can detect. It finally worked loose from the glass, probably due to the GDA on the glass, and began floating around the tank. So, I removed it at noon - I consider it to be a success!
Hey, that looks neat Dennis! I still lack the nerve to try to blow glass. It is one thing to do that in a well equipped lab, with the right equipment, but in my garage, with flammable stuff everywhere? Now, if I could blow one with wood I would be going at it.

Rethinking my experience as a college student glass blower (in 1959), the way to do this correctly is:
1. start with a piece of 3/8 inch diameter glass tubing.
2. heat one end red hot.
3. gently blow in the other end while turning the tube around its axis so it doesn't droop.
4. Stop when you have the desired ball diameter.
5. Anneal it by gently heating the whole end area and letting it slowly cool.
6. heat an area about 2 inches away from the ball until red hot.
7. gently blow until that part flares out into another ball.
8. Anneal it again.
9. heat between the two balls until red hot
10. gently blow - very gently - while bending the tube about 135 degrees angle. The blowing is to keep the tube from collapsing.
11. Anneal the whole thing again.
12. The hard part: use a diamond point tool to scribe a cut arount the second ball, so when it snaps off there you have the desired flare left.
13. Heat the cut edge to round it
14. anneal the whole thing one last time.

And, don't forget the very first rule - buy lots of glass tubing so the tenth try will finally all work out well!
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Glass is a good insulator, so you can have one end of a glass tube at glass melting temperature - red hot - while 6 inches away or less, the glass isn't even warm. That's why you can blow glass safely - just never suck instead of blowing. And, you don't really blow, like you would blow a balloon, you just move some air in to reshape the molten glass. It is extremely easy to blow a hole in the end if you blow hard at all. Another secret is that if you just closed the end of the tube by melting it, then tried to blow a bubble there the glass would get very thin and break. So, you need to first thicken the end a bit I recall they use a carbon block to rub the end to push it back to thicken the glass. If you do this in the middle of a tube you just push the end of the tube back towards your mouth and that thickens the glass a bit. It is fun and it is easy to just blow a simple ball, but very tricky to get much more complicated.
The only good reason to have the bulb is so it holds enough distilled water/indicator solution so you can easily tell what color it is. Otherwise it functions with or without it.
Seems to me like its still blue beacause its doing its job.... That is, if it's made correctly and allowing for the two solutions to reach eq with each other. It would indicate that you dont have enough CO2 dissloved in your tank. *hint* the whole point of having a drop checker ;) to be able to moniter a general estimated amount of CO2 in the water..... if its blue not enough... green means good to go, yellow.... well Im still playing with that one, for me yellow doesnt always mean to much CO2.... but in general your fish are going to let you know about when there is too much
Those of us who were believing the pH/KH/CO2 chart and thought we had plenty, if not too much, CO2 in the water, can now tell if we really do have the 30-40 ppm we should have. And, most of us will have to crank up the bubble rate to get there - to get the blue to change to green. That is the advantage of this method - it truly is an accurate way to measure the ppm of CO2 in the tank water. The only errors will be our judgement of the color green, and our mistakes in setting the distilled water KH at 4 or 5 dKH. We can reduce the effect of those mistakes by being very careful in how we judge the color and the KH of the distilled water.

When the bulb is yellow, with 4dKH distilled water, that means a pH of about 6.0 to 6.2, or 75 to 120 ppm of CO2! That is too much! I doubt anyone believing that even 75 ppm is tolerable in the tank. Of course if the bulb is only slightly yellowish green, the ppm may still be ok.
Wow! That is a neat way to make one of these. How much did the materials cost you? I wonder if a TAP plastic store would sell such small lengths of tubing? I know you can buy a foot of most of their tubing sizes, but I don't think you can an inch. Acrylic is a great plastic to work with since it is so easy to glue.
That's very clever. Well done. A suggestion though, next time try painting the inner tube white so that the color of the indicator is easier to see.
TAP plastics sells white acrylic tubing I think. If so, that would work best of all.
My wife occasionally has artificial finger nails "installed", and they are built up using acrylic plastic. She uses ordinary nail polish on them, so if you use white nail polish (is there such a thing???) it would work fine on the acrylic pipe.
This's My Diy "drop-checker"
Is that a shot glass? How did you make it? Once you understand how simple this device is, there must be a dozen ways to make one. The absolute simplest I have heard yet is to take a plastic tube, bend it into a "U" shape and cap one end. Of course a suction cup is still needed, but there are lots of options for that too.
OK, while I am discovering that I really like to melt glass (maybe a new hobby for me. I can be a double threat!) I just don't like the uncertaintly of this. The whole yellowish, greenish thing is just to much for me.

So, I give you the electronic drop checker:
Dennis, how did you seal around the probe, to keep the air from leaving the drop checker? Incidentally, you beat Tom Barr to this! He has been posting about making one of these by mid December. The only non-fool-proof part of this design that I see is the electrical interferrence issue. How do you satisfy yourself that the probe is not being affected by interferrence?
I wait with bated breath to see what the effect of 45 ppm of CO2 is on the fish and shrimp. (No, seriously, I plan to take a breath now and then.) When I first set up my ebay dropchecker the color went to yellow pretty quickly, with 4dKH water in it. And, all of the fish were gasping at the surface. So, I think there is a narrowing range of higher ppm's available to check out. Once I get my GDA problem solved for good, and my aquascape fixed - too much hygrophila now - I will switch to 6 dKH water in mine, to see if 45 ppm works for me.
I have been thinking about the electronic version - the "requirements" for the solution in it are much different from that of the indicator solution version. The latter needs water with a KH of 4-5 dKH so that the color will be green at the CO2 ppm that is desired. But, the electronic one doesn't have that need, so for that one it is best to set the KH to where the pH will be about 7 at the desired ppm of CO2, and that is at about 13 dKH. (Because most pH probes are calibrated to be right on target at 7.01 pH.) I don't understand how a pH probe works well enough to be able to figure out why your reading seems to be off. My pH probe has always been so erratic that I don't trust it at all, and it is too bulky to be used for a drop checker anyway. I just wasted my money when I bought it.
I'm not sure about that. A kH of 13 woudl mean you inject lots of CO2 before getting a pH change. That means you would OD you tank on CO2. I think better would be to use a very low kH so that the pH change happens fast and easily, allowing the controller to be more in control. I do not think it matters if the probe reading is at 7 or at 5, it will still be as accurate as the probes accuracy. What I mean is, I do not think that having a lower pH as the setpoint will compound any probe inaccuracies. Therefore, a lower kH will mean a faster response time... I think.
With a 13 dKH water reference you get:
pH - 6.6 = 100 ppm CO2
6.7 = 80
6.8 = 60
6.9 = 50
7.0 = 40
7.1 = 30
7.2 = 25
7.3 = 20
7.4 = 15
7.5 = 10

The amount of CO2 introduced into the tank wouldn't be affected by the KH of the drop checker water, nor would the amount of CO2 to be absorbed by the drop checker be affected. The goal should be to make the KH be such that around the ppm of CO2 you want, the changes in pH per change in ppm of CO2 are a maximum. At a KH of 1dKH you get:

pH - 5.5 = 95 ppm CO2
5.6 = 75
5.7 = 60
5.8 = 50
5.9 = 40
6.0 = 30
6.1 = 25
6.2 = 20
6.3 = 15
6.4 = 10

So, I conclude that the only effect of KH is to shift the pH range that is of interest, and it seems to me that the closer that is to 7.01, where you do a one point calibration, the more accurate the pH probe/meter is. (All of the above ppm values are rounded off to the nearest 5 ppm)

I also manipulated the equation for ppm vs KH and pH to find at what KH the change in pH vs ppm is a maximum - and, as the tables above show, the change in pH vs ppm is not dependent upon KH.
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Yesterday I learned that Dennerle makes this device, complete with reference solution with indicator reagent in it. They call it "CO2 Long Term Test Correct" and it is made of plastic. The reference solution (distilled water with bicarbonate in it?) has a KH of about 3dKH, to give a green indication at 20-25ppm of CO2 in the water. The configuration looks to be about that of the teardrop shaped glass one that is sold on ebay. So far I haven't seen this device for sale in the US, but it is in the UK and Europe.

Based on Dennerle's instructions, the solution in the device needs to be replaced about once a month because the indicator, which is a dye, will fade with exposure to light over that period of time.

I suppose in a few weeks someone will point out that Leonardo da Vinci first invented this device back a few years ago!
Try a web search for 'Dennerle CO2 Visual Indicator'. If this is the same product it is available.
Yes, that is it! For some reason I couldn't find those suppliers when I googled it yesterday. $17 plus shipping - not too bad unless the shipping cost is exhorbitant.
Here is a simple way to DIY this, using clear acrylic tube in 1 inch diameter and 1/2 inch diameter, plus two acrylic discs 7/8" in diameter and one such disc 3/8" in diameter. Tap Plastics has all of these shapes.

The advantages are:
The air gap has a maximum area and minimum length to decrease the response time.
The tube of indicator solution is small enough to take very little solution, but is easily viewed in the aquarium.
It can be mounted in the tank with a "heater holder" suction cup device made for a 1" diameter tube. The clip can be easily cemented to the device.
It is small enough not to be overly obtrusive in the tank.

But, the disadvantage is that it takes a syringe with a bent needle to squirt in the solution.

I haven't made this yet, but will do so shortly.
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My drop checker fluid goes to blue green overnight, then back to green in a couple of hours with the CO2 on. I was a little surprised at how little of the CO2 is lost overnight too.

fredyk: I don't think a gas range will be enough heat, concentrated enough to allow you to bend a glass test tube. If you try it, don't put anything in the tube, like sand, or it will make it much harder to heat up the area hot enough, and it will tend to imbed into the glass. The way real glass blowers do it is to slowly push the ends of the tube to shorten the test tube, thickening the glass where it is to be bent, then very gently blow into the tube as you bend it. That is a lot easier with a longer tube, of course. If you try this, be very careful!!
Thanks Swifty, I was just wondering if there is any efficiency difference between the two designs. It looks to me that one of them has more air space inside. It seems to me that a larger internal air space would slow down the color change time, but I'm sure surface area is a bigger factor. Surface area of the tank water interacting with the air in the drop checker and surface area of the indicator solution. I'm glad to hear that my suspicions are either false or this just is too small of a scale for it to really have an effect.
Logically I would expect the fastest reaction from one with a large area of contact between the tank water and the air gap, and, because the amount of water in the bulb is so small, the area of contact between the bulb water and the air gap would be a secondary factor. I'm not sure, but I doubt that the length of the air gap would enter into it. But, a large air volume would seem to slow it down. I don't know anything about the equations that would govern the rate at which equilibrium is reached between a pocket of air in contact with water, so intuition is all I have to go on.
Last week I took a trip to Tap Plastics, where I bought a 1" dia, 1/16" wall thickness acrylic tube, to go with my existing 5/8", 1/16" wall acrylic tube, and some acrylic disks - 1", 1/2", 5/8" diameter, plus a tube of medium viscosity acrylic cement. Then I spent a couple of hours yesterday and a couple of hours today, using only hand tools plus a cordless drill to make a couple of DIY drip checkers. The first one is probably the fastest reacting one:

The second one is probably the easiest to read the color on. I used white fingernail polish to paint the inside of the air gap tube which becomes the background for the fluid in the bulb.

Tomorrow I plan to load both with distilled 5 dKH water and reagent and place them in the tank at the same time, to see how they compare. I will post those results, too.

Edit: Today I loaded them and added them to the tank.

Edit: After two hours all three of the devices have the same color. The one with the white background was the slowest to get started with the color change, by a half hour or so, but once they were all changing color, both of the DIY ones ended up with the green color at about 2 hours. Now, I'm not sure what affects the response time of these, but I am sure that both of these DIY designs work well. (Both of these have been spoken for now. Maybe someone else would like to start making these and selling them here?)
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Hoppy just currious, whats the cost range for one of your DIY drop checkers???
The cost of making one of these is hard to say. Tap Plastics, or at least my local store, won't sell small pieces of acrylic tube, so I bought 5 foot long pieces, which are about a dollar per foot. The little acrylic disks are about 50 cents each. And the cement is a few dollars for a tube big enough to make a hundred or more of these little things. The suction cups are "Lee's Heater Holders", two per package and a couple or so dollars for the package. I didn't have disks to fit inside the 1" dia tube, so I used a 1" hole saw to cut out pieces of 3/16" acrylic for those, since they needed a hole down the middle anyway. The cost of that is as near zero as you can get. I'm guessing my cost for each of these would be around $3. When I get thru with these, probably tomorrow, I will give them away for the $4.50 cost of priority mail plus PayPal fee plus $3 for the materials - $7.50, and one has already been spoken for. The Red Sea version on EBay just went for $14 including shipping, so this is still a bit cheaper, especially if you already have a pH test kit, and it's a lot cheaper if you make your own. (Providing you have a use for the left-over tubing and cement.)
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