4dKH Solution - The Planted Tank Forum
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post #1 of 6 (permalink) Old 12-21-2009, 02:32 PM Thread Starter
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4dKH Solution

I mixed up a batch of 4dKH solution Saturday. Ended up with 500ml and using API's KH test it comes out at 4 using the 5ml sample and close with a 20ml sample (17 drops).
I filled both DC's and put them in the tank and within an hour both were yellow. This morning after the CO2 had been off for 10 hours it's still yellow. For the indicator I used whatever it is that's in API's pH test kit. 2 drops and it was a deep blue.

Sounds like I'm missing something obvious.

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post #2 of 6 (permalink) Old 12-21-2009, 02:56 PM
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What size tank?
Tank PH?
Tank KH?


90 Gal, 4x65 CFL, 2 Eheim 2215, Pressurized C02
First attempt at planted
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post #3 of 6 (permalink) Old 12-21-2009, 03:24 PM Thread Starter
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I thought only the CO2 level would change the DC reading since there's only a gas exchange taking place. If those mattered it would seem to me we could just use tank water.

Tank is a 90g
pH is 6.1 to 6.9
KH is 6 to 7

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post #4 of 6 (permalink) Old 12-21-2009, 03:35 PM
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The overnight yellow color just means your tank doesn't outgas very fast. You may not have much surface disturbance, for example. I always tried for a lot of surface ripple when I used CO2, so it would outgas more rapidly at night, and so the water would absorb more O2. I don't see any mistake you are making with the drop checker. It is a very simple device, a simple method to use, and foolproof, as long as you can discriminate colors reasonably accurately. But, it will never tell you any more than that the ppm of CO2 is somewhere between about 20 and 45 ppm, and even that is only where the drop checker is located, not other places in the tank.

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post #5 of 6 (permalink) Old 12-21-2009, 03:52 PM Thread Starter
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I thought the same thing about outgassing so I turned one hole of the spay bar up towards the surface yesterday and it's causing a fair size ripple.

Thinking I might have mixed up the pH and KH bottles at some point. I've been out of the solution for a couple months and thought I might want to check CO2 again. In the past I've only used those supplied by GLA and never had this problem. DC would always be blue in the morning.

This whole thing started because my pH is on an overall decline. 4 months ago it would hang around 7.3 in the morning and bottom out about 6.5. Now 6.7 or so is top end.

If I'm checking CO2 like I am now I have a DC at each end of the tank. I don't use them all the time. Just for 2-3 weeks to check how things are going, this time since a bit of BBA is showing.

I'll just start over tonight.

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post #6 of 6 (permalink) Old 12-21-2009, 05:31 PM
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Actually, it's the build up of CO2 in the Drop checker that keeps it yellow is partly the problem as well. If you remove the dc out of the tank to let the solution turn back to blue, then put it back in the tank, you'd see a better reading.

Yellow is a bit too much though. Hope your fish are ok..

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