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Old 02-11-2013, 09:14 PM   #11
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There is probably fairly significant error in the KH test, but whenever you're measuring something (co2 in this case), your final measurement is only as good as your weakest step, and the weakest step in this process isn't the measurement of dKH, but rather interpreting the color of the drop checker. Green vs light green vs dark green vs yellowish green... It's all really subjective and not well quantified in the slightest other than green is good, lighter shades are more than normal green, and yellow is too much.

If you like, you can measure two 5 mL aliquots, combine them, and measure that such that each drop will be .5 dKH. That should milk a little more precision out of the measurement.
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Old 02-11-2013, 09:19 PM   #12
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That is what I do when I make 4 dKH solution - I double the starting amount of test liquid, so that it increase the resolution of the test kit. Of course, I was also selling it on eBay so wanted to make it as accurate as possible for "customers". If I was making it for myself, close would be good enough.
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Old 02-12-2013, 08:37 AM   #13
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I made some 4 dkh last night. I started with 500ml distilled water. Added .5g of baking soda. Tested the KH and it was somewhere between 25 & 30 degrees. (I got tired of going drop by drop at 20 and added 10 at once.) I diluted 10ml of that solution with 75ml of distilled water. That gave me a solution with 6-7 dkh. I diluted again with 50ml of distilled. That gave me a solution that turned yellow on the 4th drop of KH test regent. pH tested in at 7.6 on both the low-range pH test and high range (slightly past 7.4 on the high range kit).

After testing the solution and filling my drop checker I have a tad over 100ml of 4dkh left.

I made a drop checker from a small vial of children's nail polish, standard airline tubing, teflon tape, 3/8" ID vinyl tubing and a small suction cup. I cleaned the nail polish jar with alcohol, sulfamic acid, & a good hot water rinse - then a soak in prime for a min.

I wrapped the airline tubing that would be touching the inside neck of the vial in teflon tape to make a snug seal and pushed the tubing into the jar, leaving about 1/8" poking out. I took the larger length of vinyl tubing, cut it to about 1.5" long. I cut a small hole with a razor blade about 1/3 of the way from one end (bottom) and pushed the nipple of the suction cup in. I then pushed the top end of the tubing over the outside of the vial, around the glass threads where the nail polish cap would fit.

I filled the chamber of the vial about half way up with 4dkh solution from a 5ml test tube that had 6 drops of pH indicator solution. when filled with solution and turned upside down, so the bottom of the vial is up, the blue dkh solution sits nicely around the airline tubing in the chamber with a air pocket above the blue solution and an open airway down the airline tubing out the neck of the vial. I then fixed the drop checker to the inside glass of the tank.

I was afraid I did something wrong, as for an hour I didn't get much change in the color. The lights were on the 8th hour for the day, so the photoperiod was ending, CO2 was on, and in that hour the color went from dark blue to "regular" blue. However, today when I woke up the color had changed to some shade of green. It was hard to tell as the lights were out in the tank, but I'll see this evening when I get home.

Sorry for the hijack, I just figured a description of my construction of a drop checker might be helpful for some.
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Old 02-12-2013, 09:35 AM   #14
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Great! Can you post a pic?
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Old 02-12-2013, 09:43 AM   #15
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I'll try and get one up tomorrow. I've still got some pics of my (what I think are) micro swords I need to post as well.
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Old 02-13-2013, 08:35 AM   #16
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so based on my drop checker, with 4dkh solution, it appears my pH is somewhere around 6.4-6.6, so that would estimate my CO2 concentration to be 38ppm +/- 10ppm?



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Old 02-13-2013, 08:40 AM   #17
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Yup. Looks good.
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Old 02-13-2013, 08:47 AM   #18
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Quote:
Originally Posted by fort384 View Post
Yup. Looks good.
Thanks. So its not too high? what would be a potentially dangerous level for CO2?
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Old 02-13-2013, 09:14 AM   #19
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Over 50 and you might start to see some issues. I prefer 30-40 though a lot of folks recommend 20-30.
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Old 02-13-2013, 09:17 AM   #20
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Excellent, thanks. So far all the inhabitants look to be doing fine at the current CO2 concentration.
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