Genhydro ph drops

I have recently switched from numerous digital ph pens to the ph drops from General Hydroponics. I've noticed after 5-10 minutes the colour changes from when it is first tested. Are you supposed to read the colour as the drops are added or do you wait until the vile has stopped changing colours? I know I will get some responses stating to use a digital meter but I have found them to be to high maintenance and fragile. (I have tested a few popular meters freshly calibrated with ph7 and in the same water and they all had different readings)

PLEASE HELP ME AND MY GIRLS!!


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temps will mess with the ph so that may have something to do with it.

I put 3 drops in put the top on & shake then read.

I spoke with a tech at GH and he said to wait until it stops changing colours and nothing about temperatures

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I use them and have found they are accurate. Using multiple tests in a row and saving the first test to compare color against will help to determine a more accurate reading. Passing different colored light thru the test sample can seam to change the color. For example using your hps light can make it difficult to judge the color and get an accurate reading. I like to take my reading under my daylight color incandescent lights that are set up as a vanity.

I use the drops and let my sample sit to see if the color changes... it did not change color. It could be like one poster said where the temp is changing; do you run a chiller in a res? Even if not, the water temp could be much different than ambient temps which could cause the ph to drift as it warms up to room temp. If that is the case I would think the ph drops would be most accurate when you first look at it and the temp is the same as the res water.

Firstly, remember that pH is considered an 'immediate' test. That means you can't let it sit. It is meant to be added and read immediately. Add the drops to achieve a color change and take the first reading. Don't let it sit for 5 or 10 minutes and try to take another reading. The extra time will cause a continued reaction of residual compounds. You want to take the initial measurement when the reaction is at its strongest.

The temperature interference will occur when the (pH drops) is a different temp than the sample you are testing. They should be within a couple degrees of each other. Although the (pH drops) are likely meant to be used at 20 degrees Celsius (about 68-72 degrees Fahrenheit).
I'm going to add this scenario to my pH thread. Look for it in my signature.

Also, meters will give varying results. The reason for this is that each one has a range of accuracy from the manufacturer. One could inherently be -1.3 pH units, while another could be off by +0.7 pH units. Add in the normal biases of measurement, and it becomes understandable.