Calcium and magnesium are what make water hard(there's more to it but for this instance this works fine), you adding more will only make the problem worse.
you need a working ph pen asap. and are you feeding nutrients or just using time release mixed into the coco? coco is not a medium you want to do that with. you want to take advantage of the medium your using and in coco you have total control, unless you add a bunch of stuff to it that you can't control.
no harm in watering this one out to learn but i think you're missing some basics with your response to the
calmag question. i recommend you research more about water quality, why you would use what medium(mostly comes down to how much you want to water), and what makes a plant food complete, and how to use ppm when feeding so you know what you're actually feeding your plants and why. you can just Google my keywords in the list and find answers.
you should then grab a balanced nutrient and just that. some easy and complete ones are
canna coco a&b, gh flora trio,
dynagro grow, and many others. that is all you need to grow good weed. anything else should be tested by you and added only if the results exceed the cost. almost no flashy bottle will do this and are almost all made from the same proven ingredients that you can add for a fraction of the price by just buying the active ingredient.
don't get discouraged, it's not difficult just has a definite learning curve. you need some base knowledge. check out npk university and harley smith videos. his intro to hydroponics classes have had international success from both industrial and private growers. he teaches the basics of hydroponics and plant care very well and you'll benefit tremendously from his videos.
but absolutely keep this plant and try your best. those experiences are invaluable.
