Soil PH

I'm not a big fan of the strips and drops. Sometimes they're hard to read, especially when solutions tend to be stained from ferts and runoff muddied by soils. You can order a digital pH pen for like ten dollars(US) that makes life much simpler.

These are for testing liquids, so you can only measure water that you pour or that drains away. Draining water tells you more, but it can only be measured when your plants are big enough, so that you water to excess at the bottom. About 30-50cm, depending on the amount of soil present. Otherwise, you can measure your finished nutrient solution/watering water to know how much you add. You have to keep in mind that there are many organic nutrients in the soil, and also excess fertilizer from previous feedings that lowers the pH. Optimal is, in my opinion, 6.2-6.5, but I would water around 6.7-7.2 due to the organic nutrients in the soil + fertilizer deposits. But I believe opinions differ on these numbers and it also depends on the setup; they should be enough for orientation.

These wont get you far determining the Soil PH they are more for the liquid types.

In future, if this is hard to read, get the 4-color one and it's easier to differentiate the colors. You can do 2 things. Dip it into runoff -- try to be consistent with how much runoff you get and when you dip it in. Sooner will be dirtier and more elevated EC and possibly a different pH than what is actually in the substrate -- this will always be true with runoff, but if you take th emeasurement in the same way and form a good baseline while the plant is healthy, you know a "safe" range even if it isn't what you expect it to be based on how youfeed or what 'they' say it should be in the rootzone. Runoff is always offset. Soil slurry -- same drawbacks. Awlays an offset and that offset depends heavily on your method. Don't take soil from the very top, as no roots shoudl be in the top 1-2" anyway and if they are tehy are ineffective roots most of the time due to exposure to light. So, always take a same amount of substrate, always add the same volume of known pH'd water to it to make a slurry. 7.0 pH is wise to use. Expect it to read a bit higher than reality of the substrate in this context. (runoff above is likely more acidic than the root zone is, so this is opposite in most cases, since the substrate should be slightly acidic to start) this is as much art as science. Be consistent with how you take readings and that will help a lot - even if you don't do it exactly like i suggested. you need to learn what "normal" is before reacting to these readings. Hopefully you can see what is normal with a very happy plant over a long period of time to form a proper baseline to compare to.