No3 you say you are lowering the pH to 6.5 for a coco grow. Is it just coco or do you mix it with organic stuff?
Reason I ask is coco on its own has a pH of about 6.0 and that's the middle point for setting pH in veg and typically the lowest in flower...ive been using a middle point of about 6.15 in flower.
I haven't used vinegar before to adjust pH but reading up on it now it says it is stable short term for around 3 days, but I've found that stability changes with nute types. I'm using lemon juice and getting 7+ days stability with my mix. Apparantly phosphoric acid and sulphuric acid are the go, phosphoric being the safest.