When you have a filteration problem on your hands or when your aquarium is undergoing cycling, you may reach the highest reading limit of your testkit. If you need to overcome this limitation, there is a simple way.
1. Look at the marking on the testtube which shows the level
the water sample should be.
2. Measure as accurately as possible the height of the testtube from the base to that marking.
3. Divide the height by 2, and mark it with a small piece of tape.
4. Collect water sample from your aquarium and fill it up to the place you marked.
5. Top up the rest with RO water(reverse osmosis water) or distilled water until the original test tube marking.
6. Do the steps for determining the kit reading as usual.
7. Take the result of this test and multiply it by 2, and that will give you the real reading.
For example, if the result of the test is 80ppm, then your real reading is 160ppm.
If the result of the test is again at the maximum before you multiply, you should redo it, this time filling the testtube 1/3 with aquarium water and 2/3 with RO/distilled water, then multiplying the end result by 3 instead of 2. If it is again at the maximum then you can fill the test tube 1/4 with aquarium water and top up 3/4 and multiply results by 4.
Note: This does not work for pH. To overcome the limits
on your pH testkit the only way is to use an electronic pH tester (pH probe/pH
pen/pH meter) which has a larger range.
If you cannot get your hands on reverse osmosis water or distilled water, you can use mineral water. However, if mineral water is used then this method should not be used to measure KH and GH.