Wooooord I use the exact same nutes! Haha Jack's Classic 20-20-20 for vegging, and the 10-30-20 for flowering. I'm not really sure what you mean by "diluted by 1/4". The directions on the back will give you some good guidelines. However, the amount of nutes you can use depends on numerous things (i.e. - indoor or outdoor, what kind of lights used if indoors, grow-medium used, size of containers, the strain and overall genetics of the individual plants.) My plants are outside on nice days and inside under cfl's on crappy days, each plant in a large container with potting mix: For "half-strength" I add about 1/4 teaspoon of the nutes to a gallon of distilled water. For "full-strength" I had at least 1/2 teaspoon (if not more). When my plants are old enough to handle nutes, I run them through a cycle (Half-power the first water, Full-power the second water, Half-power the third water, Flush with distilled water on the fourth water.) Make sure you take note how each plant handles the nutes during the first-cycle, and adjust the dosage accordingly. When flushing, make sure you add about 50% to the watering amount (so if you normally add 1 gallon to each container, flush with at least 1.5 gallons).
But with all that being said, I'm pretty sure coco growers are supposed to keep a lower pH than soil growers. But either way, the only way to find-out what dosage is best for YOUR plants is try a cycle. Good Luck! Keep us posted!