something wrong... with Ph I suppose

Hi! First time growing hydroponics (bubbleponics)... growing under fluros, temps and the rest is okay, except the Ph of the water. How come I cant get it under 7? I added some vinegar to lower it... but in few hours its back to the previous (7.7-7.9) again plants are suffering a lot. what should I do? I read somewhere that Ph should fluctuate no more than 0.5 in 24h time or smth. Should I just change the WHOLE water tank with fresh water and not try to balance the Ph of the water in the water tank as it is now. My Ph is so high that my plants are wilting and dying. At first they showed lack of nitrogen having very bright green/yellow leaves.

You could pick up some Nitric Acid pH down solution from a number of online dealers for like $10 and just be done with it. I'm sure you've used enough vinegar at this point, all you need is some fish and chips. Nitric Acid holds pH better than phosphoric acid pH down. Vinegar can be used as a herbicide... So... Yeah. Get yourself the right stuff, you will be very happy you did.

How are you testing your pH?