I have used this range for 4 grows and had no issues (Well I had one issue but it was because I didn't have a meter for 4 days and used tap water with a ph of 7, as soon as i went back to 5.8 the issue disappeared).

The watering frequency for coco depends on how big your pots are. I use really small pots and water everyday (not ideal but it works for me), with larger pots it is every 2 or 3 days.