15 ppm co2 drop checker - The Planted Tank Forum
 
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post #1 of 9 (permalink) Old 11-23-2017, 01:08 PM Thread Starter
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15 ppm co2 drop checker

Id like to lower my threshold for co2, would halving the baking soda in my 4kh solution make a2kh solution? I suspect that's a big yes, but would that change color at 15ppm co2? Sorry if this post should be in water parameters. Also is anyone else super worried about checker cleanliness issues skewing results?


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post #2 of 9 (permalink) Old 11-23-2017, 03:04 PM
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Yes: half the baking soda is half the dKH. Do you make your dKH solution by diluting a large quantity of high dKH, which will give more accuracy? Example; making a 20 dKH solution in 3000 ml and diluting it down to a 2 dKH solution. The lower (smaller) you go, e.g.; from 4 to 2 dKH, the more difficult it is to be accurate.

The color change would still show correctly (remember that these color changes only approximate ppm levels). However, if you look at the standard pH/KH/CO2 color charts, you will see that, at 2 dKH, the ~15 ppm area of CO2 is just over the blue line into the lower end of the green region. So, you will want to adjust CO2 to catch that sweet spot where it just changes from blue to green. That will take some playing around because it will take 3-4 hours for a drop checker to respond to CO2 changes. Even then, you are probably going to be dealing with a +/- 2-3 ppm tolerance.

You should change your solution every week or so. I change mine every other week. They can get stale and will tend to not change color as readily when the CO2 drops. I use small (2-3 ml) pipettes (100 for $5-$10 on Amazon) to flush them clean with distilled water before refilling.
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post #3 of 9 (permalink) Old 11-25-2017, 06:47 AM
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I only make 4 dKH water, then simply use a measured syringe to mix with RO to the KH I want. For 15 ppm target, I just mix 5ml of 4 dKH with 5 ml of RO, and inject into my dropper.

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post #4 of 9 (permalink) Old 11-25-2017, 01:46 PM
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Quote:
Originally Posted by natemcnutty View Post
I only make 4 dKH water, then simply use a measured syringe to mix with RO to the KH I want. For 15 ppm target, I just mix 5ml of 4 dKH with 5 ml of RO, and inject into my dropper.Sent from my Nexus 6 using Tapatalk
I prefer to make a large 40 dKH solution and then dilute it to 4 dKH in order to increase the accuracy which, theoretically, should reduce the risk of being too far off in the color change of the final product. The color change is a vague thing anyway, so anchoring it in a more precise dc solution seems best.

I Add 2.4 grams of Seachem Alkaline Buffer (baking soda can be substituted at a different weight) to 2 Liters of RO/DI water. I then add 50 ml of this solution to 450 ml of RO/DI water. This new solution will have a 4 DKH. This will last a long time if stored in a tightly sealed container. If any evaporation occurs, KH will begin to rise.
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post #5 of 9 (permalink) Old 11-26-2017, 01:45 PM Thread Starter
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Ok, so i definitely need to use 20k stock solution and dilute to 2k at use. I will be using baking soda as its what I've got. Also shouldn't e assume that our distilled water has a ph of 6? The di water will be the same deal ph 6 if it went through an ro system first. Any distilled I've ever bought measured acidic when tested, its reacted with co2 in the air. I assume that no one here is using highest quality non atmospheric distilled/di water. I assume that any manufacturer of drop checker solution will adjust for those things, but i am doing this in my kitchen. I am only getting crazy about this because I've tried to reduce my solution volume/raise air volume to get faster reaction times in the checker, and all mistakes will make larger differences.


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post #6 of 9 (permalink) Old 11-26-2017, 01:48 PM Thread Starter
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Ph 6 is an average, it sounds like it can be as low as 5.5 but the test doesnt go that low


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post #7 of 9 (permalink) Old 11-26-2017, 02:35 PM
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Distilled water has no buffering (zero KH), so pH tends to appear acidic as CO2 moves in. You can never hold the neutral 7 without lab-grade equipment, but itís not necessary. If you want to increase precision, you could put an aerator in the distilled water for 24 hours so the CO2 equilibrium point is reached and then create your 20 dKH solution. Although I doubt that it would make a noticeable difference in the drop checker, it would make the batch closer to the original over time (for storage purposes), assuming you donít get evaporation. If you really want to increase precision, the way to do it is to get a better alkalinity test kit, such as a LaMotte, but those are around $50. Since a dc isnít that accurate anyway (e.g.; what shade of green equals 15.67 ppm of CO2?), I wouldnít worry about such fine details.
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post #8 of 9 (permalink) Old 12-02-2017, 02:26 AM Thread Starter
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Ok well i was as careful as i could be, my test kit put my solution at 18 dkh. Close enough! Here's a shot of my diy checker, its just the bottom an api test tube and a cut off pipette, and a touch of silicone. It takes .5 ml of solution. I dont have one handy but it will be pretty sleek with a thermometer suction cup holding it to the tank


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post #9 of 9 (permalink) Old 12-02-2017, 02:28 AM Thread Starter
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Just needs a suction cup
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