Help! Going Out of Town!

[Cannabliss89]

So I have two clones that are in one gallon pots, one is about two weeks old and one is about 3 weeks old since I've potted them. I'm going camping for almost 2 weeks and have a few questions. I've been leaving the pots outdoors all the time so they are used to it, since they will be outside the whole time I am gone on my trip. My brother will be stopping by every 3 to 4 days to check on the house and to water the plants. He is a smoker but hasn't ever grown before so he doesn't know/realize the amount of care these girls take. So I'm going to try and make it as easy for him as possible. I don't want to make him balance the ph of the water every time he waters them like I've been doing, I was trying to make it easier for him, that way he can just water when they need it and everything will be good. He can also send me pics of problems if they arise.

So my plan was to go to the store and buy one of those 5 gallon jugs and fill it up with that filtered water they have at the store. Then I'll take that home, check the ph and add some white distilled vinegar until the ph is around 6.5. Then I'll have 5 gallons of ph balances water, and that should last him to water. my question is, will the ph stay at 6.5 for two weeks? or will it fluctuate? Can I get away with this? Or would he still have to test the ph every time?

Any other advice to make it easier for my plant watcher? Any help would be great I leave in like a day so please help if you can.