Need help with Hagen Kh/Gh test
I hate these stupid color tests.
I am doing the Kh test, and your supposed to add a single drop of reagent, and then add a drop at a time until your solution turns from blue to "yellow/lime" color. On the back, where you are supposed to match the color, its got a blue square for start, and a yellow square for finish. At 8 drops my water turns from blue to a greenish color, and at 10 drops its the yellow on the back, so what is my Kh? Anyone who uses this tests please give me some insight as to what is accurate. 
Your answer is on the back of the last page in the directions.
Well here goes: The yellow color is your end color for the KH test. You multiply the number of drops used to get the yellow color by 10. It was 10 drops in your case. This gives you 100 mg/L or 100 ppm. If you want to convert ppm to degrees, you multiply your ppm value by 0.056 to get degrees. So 100 x 0.056 = 5.6 degrees. The GH test has a little different formula. As an example, let's say that you used 10 drops to reach the end color of light blue. For the GH test, you multiply the number of drops used to reach the end color by 20 instead of 10 like the KH test. In this example, this gives you 200 mg/L or 200 ppm. To convert to degrees, you again multiply by 0.056. So, 200 x 0.056 = 11.2 degrees. You can get degrees from ppm another way. Divide your ppm by 17.86 to get degrees. Note that both KH and GH are measured in CaCO3 equivalents. I hope that this helps. 
thanks a lot ... you helped more than you know

I don't have a KH tester, but mh GH tester says to keep adding drops until it changes from yellow to green (shaking each time). Once it changes to green, count the drops and look at the GH chart for the different fish you have to make sure it's in the right range. On my kit you multiply the drops by 17.9 and get your Parts Per Millon (ppm) or percent GH in the tank. I would guess by the lst post that KH has a similar method. For example, it took mine 13 drops times 17.9 is roughly 230 ppm. This is actually rather high. Frequent water changes should fix this though eventually.
as far as accuracy, you are only going to be accurate to the nearest drop. 
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If you round 17.86 degrees up to one decimal place, you'll have 17.9 degrees. You can have two ways to calculate ppm and degrees. If you take 1 and divide it by 17.86 you get 0.056. Also, if you take 1 and divide it by 0.056 you get 17.86. Then, 17.86 ppm per degree and 0.056 degrees per ppm are your constants. So, let's says you have 5 degrees of hardness. You can multiply 5 degrees by 17.86 and get 89.3 ppm. Here's the other way to do it. Let's use 5 degrees of hardness again. You can divide 5 degrees by 0.056 and also get 89.3 ppm. Let's deal in ppm this time. Lets say that you have 100 ppm. You can divide 100 ppm by 17.86 and you get 5.6 degrees. The other way is to multiply 100 ppm by 0.056 and you get 5.6 degrees. Do you understand what I did in these calculations? Here's a tip. Both of these test kits use 5 ml of water for the test. You can be a little more accurate if you can find a test tube that will hold 10 ml of water. When you get the end color, you divide the number of drops by two. This may help if you have trouble deciding where the end point actually is. I believe that Tetra and Red Sea use 10 ml test tubes in some of their kits. (You can also use 15 ml, 20 ml, etc. also. Just be sure to divide by the number of drops correctly.) LaMotte's alkalinity test kit is more precise and it's about $20. It's a good one though. It's color change end point is rather abrupt. That helps it to be more accurate. LaMotte KH/Alkalinity Test Kit 4491 DR / Direct Reading Titrator Method  Marine Depot  Marine and Reef Aquarium Super Store 
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I know that when you got the yellow/lime color, it was confusing. That means that you were almost to the end point. You had to add two more drops to reach the end point. Deadmonkey asked some related questions. If you get a chance, please read my reply. 
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This allowed me to use my test. I lost my booklet and no longer had the color chart, or the directions. I got on here looking for this information specifically. Thank you 
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