Why 4dKH ? - The Planted Tank Forum
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post #1 of 3 (permalink) Old 05-02-2013, 04:02 PM Thread Starter
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Why 4dKH ?

So, I've seen all over the place to use standard 4dKH from bicarb for the drop checkers and I'll be using my analytical balance and DI water to make it up (0.12g sodium bicarbonate or 120mg / 1L). Just to do it I used the tank water as suggested by the drop checker literature knowing that various salts would be interferences for accurate readings. Immediately both drop checkers turned dark green and have not budged. Is this the reason why we shouldn't use our ambient tank water in the drop checkers ?

So, is it suggested to use 4dKH standard as opposed to using something more ball park to where our ambient KH is for our systems ? What's the relationship of 4dKH being specified ? Mine consistently checks out to be 6-8 KH (whether I titrate 5mL or 10mL and before or after a water change). I've not yet begun to dose EI and just started CO2 last week and am gradually working into these processes. My pH is now 6.8-7.0 depending on the time of day. This in theory should put me at ~30ppm CO2 (ball park). Why would I not create a 7 dKH drop checker soln standard ?

I also saw where someone had a concern about making their own 0.1% bromothymol blue indicator soln in ethanol. Why would you be concerned to do this rather than try and solubilize it in 10M NaOH ? We're talking 5-6 drops of ethanol in a large volume of tank water (comparatively speaking) if the drop checker ever broke in the tank. I'd believe the LD50 of the bromothymol blue to be higher than the ethanol at it's concentration in the tank.
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post #2 of 3 (permalink) Old 05-02-2013, 04:11 PM
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at 4dKH you have 30ppm at green on the drop checker...just a color thing.
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post #3 of 3 (permalink) Old 05-02-2013, 05:17 PM Thread Starter
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Good deal. Thanks !

Just made up my 4 dKH & 0.1% indicator soln in the lab !

Tested it by breathing into a sample soln using a pipette....fun to watch it go blue, then, green, then yellow so quickly. Then took another sample and added one drop citric acid to turn yellow floowed by one drop KOH to turn back blue. Oh the fun of having a lab !
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