Leaf tips turning yellowish brownish

Well, first of all, if you're growing in coco, the substrate needs to be kept moist all the time... Growing in coco has been called "hydro in soil" ... so you can't really overwater! In any event, even in soil, overwatering does not produce these symptoms... What you've got is probably a combination of a potassium and phosphorus deficiency. Your pH (I've looked at your diary) is perfect so that's not the problem.... You're making your own nutes so I would tell you they need more of both P and K... bonemeal would be good for the P and Langbeinite would be super for the K.... With Langbeinite, since it doesn't dissolve very well, when I grew in soil I would just use a tablespoon of it as a top dress once a month... and I used it throughout the grow. Good luck!