To my eyes, I see what looks like a combination of issues. It looks like they are running way short of nitrogen and possibly calcium and magnesium. Looking at the pots in the pictures, it appears that they are getting too dry. Also that soil looks to be too dense. Now this is just from what I can see in pics without being there. Often, if the plants get too root bound and allowed to get dry too often because of being in small pots, the roots will push to the top of the soil and make it difficult to water them properly where the deeper water roots get watered properly. Also the inner part of the root ball ends up getting dry from not getting water penetration into the center.
I can see pearlite in the soil so it shouldn't be getting too dense. But it looks very dry. Iff the roots get dry too much, too often they will lose their ability to take in needed nutrients to keep the plants going, and they will then begin to falter.
What nute brand are you using and do you use any additives? It is important to have a source of calcium and magnesium in the soil because most nute brands don't add much to their mixes because the calcium and magnesium can bind with other nutes and become insoluble where they can't be taken in by the roots. I always add some dolomite lime if I am growing in soil, and I use a liquid calmag additive for soilless and hydro.
when do you begin adding the nutes after setting your plants in the happy frog soil? The Happy frog is supposed to feed the plants for 3-4 weeks but then after that, the feeding is up to you.
How often do you feed and water? Do you feed every time you water or do you skip? Many times people who grow in soil will do a schedule of feed, water, water, feed. You should water often enough to keep the soil from drying out but not too much where it can't dry some. You want to allow the soil to dry some so that it can aerate itself but not so much that the roots begin to dry up.
How much water do you give them each time? Hackerman has been having a similar problem because he wasn't watering enough to thoroughly soak his medium before allowing it to dry again. You must give them enough, and give it to them slowly enough for it to thoroughly go through all of the medium to prevent dry spots from occurring.
How old is your pH tester and how often do you calibrate it? the pH testers must be maintained well or the bulbs will get out of calibration. It is important to keep them stored in a proper solution every time they are not in use so that the bulb doesn't dry out or it will never read right. You also don't want to use old or contaminated calibration solutions as they can cause your meter to be off. All it takes is for your pH to be off half of a point to cause you problems with the plants and nutrient absorption. Typically you want to keep soil pH between 6.4-6.7 but for soilless, you would keep it lower between 5.9-6.3
