Read and article or two from a reputable source. Literally could write a book answering your question.. and they have.

should come with instructions on how to callibrate... simply push a button, dipin a baseline solution or 3 and it's good to go. keep track of what you mix... you dont have to pH test every time. Spot checkign is good though, or when you see symptoms is also a good time to check.. when everything is going well, not much reason. In 4 ytears, my tap water changed drastically 1 time.. it killed 75% of seeds sowed bc i was adjusting pH of tap water down to 6, or so i thought. my tap shifted from 8.4 to 7.0. So, as long as the inputs don't change, pH will be consistent based on the products you use.. if it needs 3mL or acid or base to correct pH, it will always need that amount.. .until one of the inputs change. then, you need to make sure it's still properly affecting pH. soil slurries and runoff are not a precise indicator of substrate pH... runoff is likely higher than what is in the put, for example. soil slurries will give you inconsistent information if you use differinve volumes of water.. the water you add should be a known pH so you can guesstiate a weighted-average for slurries. The more runoff that drains away and more that comes out will be closer to what is in substrate but still lagging or leading depending on context.

Throw that ph pen right in garbage they're just that garbage, inaccurate not really sure if they were properly calibrated properly but they're garbage, I would get some ph litmus paper, with a range of 5 to 8 with 0.4 incremental changes and they will give you the necessary information you need, ill post the brand I have when I get a min...As far as the TDS/EC pen it is what it is for the price it will give you a ball park reading with a bit of +or- but accurate enough to get the job done.....There are plenty of videos on YouTube to give you a tutorial on EC and TDS best practices and I would suggest starting there...Best of luck

I don't know your meters mate but they should come with some instructions on how to use them. They should also have come with some calibration fluid for the Ec meter and some Ph7 or Ph4 solution to calibrate the ph pen. Some ph pens require ph7 fluid others ph4 and some both. The Ec meter tells you how strong your solution is and the ph meter tells you the ph of the solution. Depending on your preferred growing medium to what targets you need to hit. Coco/hydro range from Ph5.5-Ph6.5 with sweet spot near the middle. Soil Ph6.0-6.8.

pH acidity of the water, cannabis plants prefer slightly acidic water, so when you take water for irrigation, you can measure the acidity. The perfect range for hemp in soil is 6/7, 6 being slightly acidic and 7 neutral. If you go above 7, you'll have alkaline water, which is less suitable and can cause imbalances in nutrient absorption. The same thing happens with water that's too acidic, below 5. To correct these imbalances, there are pH correctors, one acidic and one not. The acidic one is pH-, and the more alkaline one is pH+. As for EC, it measures the amount of dissolved substances in the water; the more fertilized it is, the higher the EC. There are ranges to respect, and I'll leave you a link that explains these things better than I can... https://growace.com/blogs/learning-center/ph-and-ppm-knowing-what-your-plants-are-eating-and-how-much-they-can-handle

Msweedster they came with a manual with directions. I suggest reading it to properly use and store them.