a couple of notes...AN or gh 3-part, pure blend pro will buffer your water close to correct ph if you are using RO or distilled water...In other words, I find that almost all, not all, but almost all the time...If using Pro nutes and RO/distilled water...you will get well within the ph limits required to grow successfully...

You need a PH pen...Hawk ebay and find one for 30-40 bucks...I got my Milwaukee(the best) for about 40 bucks and have used it for about a year. with no problems.

If they look healthy they are...

On the subject of vinegar...It works, but if you use a Pro PH down (10 bucks a qt.) then you won't have to adjust your ph everyday, because when you get your set-up dialed in, your ph stays consistent.

consistency is the most important issue when trying to achieve a good potent yield of fem's/frost...therefore ph consistency through the use of at least a good 3-part and pro ph product's is mandatory if you want to be successful growing in Hydro...If you use tapwater, you will have more ph problems because of unwanted minerals in the water.
hope this helps.lw