Dont use foxfarms....take my word for it, have i ever steered you wrong? imho, they are tomato nutes and you will see a difference in yield using other nutes....for cheap price with great results...get gh3 (general hydroponic 3 part)
get you some superthrive... its in season at walmart right now... (however, you dont need to use superthrive in flower...only in veg)
get you some cal/mag ( a must, especially for coco as its a cal/mag hog)
then if money permits, get you a flower booster....something like hammerhead pk 9/18 or an alternative. it will swell your buds.
last but not least...those bugs you seen are probably not spidermites. they are probably more gnats than anything. gnats love coco. they like the moisture.....they wont hurt anything (unless you have a hugggggge infestation...and i mean huge)
i dont sweat it, but i do use sm90 to control them...... i want to order some gognats or gnatoff or some alternative as they are annoying as fuck