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post #1 of 4 (permalink) Old 06-27-2005, 09:52 PM Thread Starter
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Newbie Testing question

Ok guys, as I've mostly only dealt with fish in the past I haven't had to run too many tests at all and pin point accuracy wasn't an issue either. Now that I'm delving into plants I'm trying to get a better feel for my water parameters so initialy I'm doing some testing and hopeing to later on just be able to use the EI method and have little worries (fingers crossed).

Until that point though, I've got a question about how to read the tests. Duh, compare the colors to the color charts right? Right. But Maybe my vision is going but its very difficult for me to match a real, test tube color to a printed color even when holding the tube against a white background. Let me be more specific with an example.

I'm using an Aquarium Pharmaceuticals GH test kit (among others) and you add one drop to the tube. The sample should turn blue, then with subsequent drops it should shift to yellow. First off, with my KH kit, I see a definate blue shift but the yellow part is still a toss up for me. My biggest problem is: How yellow is yellow? We talking just a hint of yellow tinting the water just a hair, or are we talking a -definate- 'brite' yellow? Another related question is how to look thru the test tube... do you look at the cross section or do you pop the top and look down thru the tube? Looking thru the tube is definately a darker color for obvious reasons... looking thru more liquid.

Hope someone can clear this up for me. I feel a bit silly asking such a base question.

Thanks,
Blake
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post #2 of 4 (permalink) Old 06-28-2005, 12:58 AM
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you are looking for any change at all. With gh and kh test kits they can be made more accurrate by using 10 ml of water instead of 5ml. you then divide the # of drops by 2 when testing in 10ml of water

as far as reading the ranges that is what is tough about testing, I hold it up to the light then to the chart with background light. You should also make a calibration solution for your test kits like NO3 set to 10ppm and that way you know what 10ppm should look like.

If you have a woman in the house have her look at it they are always better with color then men


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post #3 of 4 (permalink) Old 06-28-2005, 01:36 AM
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Hi Weaver, I sympathize because I have a hard time reading those color gradients as well. These are not silly questions at all.

GH and KH are actually the easier tests to read (compared to the others where you use the color cards). After getting a hint of yellow, I usually get to a solid yellow when I add one more drop. I would just take the reading as between the two. For example, if I get a shade of yellow after 7 drops and a solid yellow after 8, I would estimate it as 7.5. You can also use the 10 ml method suggested by bigstick to give you a more accurate reading if desired.

When looking through the test tube, do it from the side, not down into the tube. When using the color cards (e.g., for ammonia, nitrite, nitrate, etc.), hold the test tube right up against the card. If there's any gap between the tube and the card, the color looks a little different (due to light coming from behind the test tube).

You may already know this, but I find it a bit easier to read the color cards under fluorescent lighting as opposed to incandescent.

Hope this helps.
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post #4 of 4 (permalink) Old 06-28-2005, 01:42 AM
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On the GH and KH, I'll sometimes look through the side of the tube, and sometimes down from the top. IME, once the drops reach the 'final' color, it won't change any more. So, in the GH, if the color looks greenish after 10 drops and the next drop makes it more of a yellow, then I say I'm at 10.5. Typically more drops after that yellow color won't continue to change it.

As to matching against a chart, I try to ask my wife or my daughter. I have lots of trouble with the pH chart...all of the 'in between' colors. I also have trouble picking the best match on my LaMotte NO3 kit. I don't question the LaMotte kit...just my ability to figure out which 'shade' is closer.
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