DIY CO2 Drop Checker

I decided to undergo the arduous and exhausting process of designing, engineering, and constructing a homemade CO2 drop checker. The process went something like this:

- Scrounge kitchen cupboards for something appropriate: 45 seconds.
- Discover two shot glasses, one of them half the size of the other: 1 second.
- Test liquid holding capacity of each by using for the designed purpose (My favorite part) : Filling took 3 seconds, emptying each about 1 second.
- Repeat liquid holding test of each in the interest of scientific accuracy: 4 seconds.
- Just to be sure, triple check liquid holding capacity (one can't be too careful with these things): another 4 seconds.
- Take a break for the evening. I wasn't about to get much more done that evening anyway. :dance:


- The next day, restart the process. Considered re-testing the liquid holding capacity but fortunately thought better of this. Washed, rinsed, re-rinsed, re-re-rinsed and thoroughly dried the shot glasses.
- Dig through kitchen junk drawer for tube of silicone and suction cups: 1 minute.
- Place glob of silicone onto side of smaller shot glass: 10 seconds.
- Push side of smaller shot glass onto inside of larger: 10 seconds.

Whew! This is getting exhausting, bear with me here.

- Push glob of silicone each of two suction cups and mash onto side of large shot glass: 20 seconds.

-Done!! Now to wait for the stuff to cure. Package directions say 24 hours to cure fully, so I wait 48. Total elapsed construction time: 2 minutes and 38 seconds. Needless to say, I was exhausted after this so I figured I'd better take the rest of the day to recuperate. Fortunately, I used up my shot glasses, otherwise the recuperation may have taken considerably longer.

Here it is after construction and in action, with carefully prepared 4 Dkh water and some Regent. Regent is still blue as this shot is right after I stuck it on. We'll see how it does in a couple of hours.

ChicoRaton said:

Wow. I have seen plans for these, but never have I seen such a simple, innovative design. Makes me nervous though, wouldn't want that falling off and spilling indicator all up in yo water, dawg. I'd put it on the bottom so it has a bit of a failsafe.

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Yes I've always wondered about possible accidents with drop checkers putting chemicals in the water as well. I emptied out some of the solution so there is just a few ml in the bottom. Mostly of course it's just distilled water with a teensy bit of baking soda so that won't hurt anything. Two or three drops of regent probably won't have much effect (I hope) on the tank should this (or any other) drop checker somehow fail and mix in with the tank water.

son2fu said:

im kind of confused, what does this thing do?

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Short answer: It's for determining how much CO2 is in your water.

Long answer: If you have a planted aquarium it's fairly important to use one of several methods to inject CO2 into your water for good plant growth. Too little CO2 and your plants won't grow well, but algae might. Too much CO2 and your fishies won't like you.

Unfortunately, there is no quick and easy test to directly measure how much CO2 you have dissolved in your water like you can with ammonia, etc.

You can measure it indirectly though. One of the effects of CO2 in your water is that it will change your ph due to the carbonic acid it creates. The more CO2, the more acid your water becomes.

Ah ha!! you say. So all you have to do is measure your ph and you'll know how much CO2 you have!!

Well, yes and no. As usual, it's more complicated than that. Many things in your tank water have an effect on the ph, or will buffer any other things attempting to change the ph, including dissolved minerals, use of peat or driftwood, the kh (carbonate hardness) of your water, etc.

One of the more popular methods of determining CO2 is to use a chart comparing your kh and your ph and using this to figure out how much CO2 you must have. Unfortunately this doesn't take into account all of those other factors so it is wildly inaccurate.

The obvious way around this is to use a very controlled clean sample of pure distilled water with a carefully measured amount of baking soda to get an exact known kh number. Then you can determine with fair accuracy your CO2 levels by measuring the ph.

This doesn't help much though since you want to measure tank water, not some other sample of pure water.

However if you take a sample of this pure water with some ph regent in it and put it into your tank but separated from your tank water by a small enclosed air space it will contain exactly the same level of CO2 as your tank water after an hour or two due to the properties of CO2 and how easily it goes into and out of water. Then a quick glance at the color of your ph regent will tell you how much CO2 you have.

Most people shoot for roughly 20 to 40 ppm of CO2 in a planted tank. If you use exactly 4 dkh water with some ph regent that will give you a nice green color when you have around that much CO2. A blue color means too little CO2 and a yellow color is a warning that you have too much.

There's a few different commercial devices and a whole lot of DIY devices that accomplish this. This is another example of one of those. You leave it in the tank and use it to find out how much CO2 you have at a glance. The downside is that it does take an hour or two to change color after a change in CO2. The upside is that it is much more accurate than some other methods.

DeMonZ said:

It's a drop checker. Basically, when it drops, it checks to see how shatter resitant your tank is.

No, seriously though. I read a post, on another board I think, where a fella made a Co2 diffuser using a large shot glass. It fell and cracked his aquarium glass. Just something to consider.

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Ouch, that would suck. Probably not too likely though. If it fell it would likely just land on the substrate and I doubt it would break.