DWC pH help please!

im growing 4 plans in a 10 gallon container...DWC. My pH keeps fluctuating. I use vinigar to bring my pH down to 5.8-6.0 and within 2 hours my pH goes back to 7. Is this a problem with the water, nutrients? I really don't know. I use Duchtmaster Gold nutrients. Its just been something I haven't been able to figure out. mabye my pH tester might be bad but I doubt it... I just bought it like a week ago. Any know what maybe going on here?

have you tested the ph of the water your using?

sirus17 said:

have you tested the ph of the water your using?

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i am not doing d.w.c at present but i remember a stage when my p.h used to change all of the time
i think the larger the res the less p.h change ,also what the less hassle ,but no expert , and now growing in coco ,but d.w.c is good. i think i just added to the wrong post sorry ???