Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
I do that (add several drops then shake) for the GH and KH tests.
When using a 2-reagent test I do shake in between. Some instructions tell you to shake and for how long, others just sort of show a picture of the test tube being turned upside down, like it is just a little shaking. Better if it is well mixed!
Other ways to alter the tests:
If you know a test will read really high (such as NO3) but you cannot read the colors, or it is off the chart, you can dilute the sample with RO or distilled water. For example, instead of 5ml aquarium water, use 1ml aquarium water + 4ml of RO. Then multiply the result by 5.
Another way: Some of the tests have you add a LOT of drops, and it is an even number of drops.
I just take half as much of a sample, then use half as many drops. Same ratio, right? Same results. Get twice as many tests out of one kit.
I would not go less than half a test tube, though. It might get tricky to see the color if there is a smaller volume. I read these tests from the side. If there is some strong color nearby the test tube might pick it up and the color in the tube might look 'off'.
Another way: I generally use the tests to compare how the tank is going over time, not to see if a particular parameter is some perfect number. To do the GH and KH tests, I can get a rough idea if something is changing by stretching the drops out. I will fill the tube only half way, then count drops like this:
1 drop = 2 degrees
2 drops = 4 degrees
3 drops = 6 degrees
This uses less reagent and confirms that things are just fine, as long as it is the same as before. And if there is a problem, I can always re-test with a full test tube and then 1 drop = 1 degree.