just now i had to add 200ml of apple vinegar in 14gallons of water to get it to 6.4ph it was 8.2 this sound to me alot but im a noob so i just wanted to get some advice,is this ok or is my ph meter maybe screwed.and is lemon juice maybe a better choice and how long can i use that water in which i balance the ph this way

Buy some pH down for $7.95 then you'll have it. Stop using vinegar, from what I hear it's detrimental to some micro organisms in the soil. If you HAVE to, use the lemons.

Checking myself on last post. Scratch the "soil" I wrote now that I reread your post seems like you're doing hydro grow. In that case definately get the "pH down" at a Hydro shop, or online, or a pool/aquarium store.