Liquid Ph test kits offer growers an inexpensive alternative to electronic probe pH meters and give results which are accurate enough to give you a basic idea of your pH range to help manage your crop.
However one thing that you need to watch out for is that it actually tests and displays the pH range that your aiming for . Many growers have come to the site with meters that only go down to 6.5 which is not low enough. Generally this is due to it being made for pools or aquarium. If you end up with one of these meters figuring out your pH level can be trickier though not impossible because often you have to guess based on what you think the colour wheel would do next if it followed the same pattern untill the start or end of the pH scale.
So when looking at liquid meters make life easier on yourself and make sure it at a minimum messures down to a pH of 6 , at least then any guess work to be done is kept at a minimal.

There are a few more important things to keep in mind when using a Liquid tester , the two most important of which i have listed bellow.

• Always use a white background when looking at the colour in the vial  A non white back ground can alter the color subtly enough that you may end up being off by anywhere from a little to a lot depending on the color in the background.

• Make sure that all color comparisons are done under natural light or normal COOL WHITE household lighting and NOT HID OR WARM WHITE light, as the red/blue spectrums of the light (HPS, WARM WHITE or MH respectively) will cause a serious change to the appearance of the solution beign tested,  in some cases
  runnign the solution an entire point off of what it should be,  simply by usineg non natural light which dfetes the whole purpose of managing your ph levels to begin with.