Get an Ec meter, keep a daily log and the increase in Ph and its relationship to Ec will become obvious to you.

Ec meter is the only way to tell nutrient strength and, as plants are using nutrient every day, it is also the only way to optimize nutrient strength.

Don't overshoot with Ph, 6.4-6.8 is good range. Also, if you increase reservoir volume, both Ec and Ph are easier to control incrementally.

As nitrogen is used by plants, Ph drifts up with hydroponic nutrients.

Acetic Acid is vinegar. Vinegar is not good to use in hydroponics. The acid wears off and the PH shift is negated. Use sulfuric acid. It is cheap, readily available and a few drops works great.

the ph will fluctuate for a couple weeks, just keep checking it, i like to get a LITTLE algae in my reservoir to keep it steady

Most hydroponic nutrient solutions have all the nitrogen as nitrate. The pH drifts up because roots absorb more negatively charged ions or anions, primarily nitrate (NO3-), than positively charged ions or cations, such as potassium (K+), magnesium (Mg++) and calcium (Ca++). To maintain a charge balance, the root excretes hydroxyl ions (OH-).

Adding a little ammonium (NH4+), from 5 to 10% of the total nitrogen, can minimize the upward drift in pH. If too much ammonium is added, the pH will decline because the root absorbs excess cations and then excretes hydrogen ions (H+) to maintain charge balance.

[Note that the + and - should be superscripts and the 3 in NO3- and 4 in NH4+ should be subscripts.]

DHershey is right on. Most hydroponic nutrients use nitrates as a source of nitrogen and the ph goes up as the plants use it. If you use a little nutrient that supplies nitrogen from ammonia or urea (MircleGro), the ph will go down. You can balance the ph without adding chemicals.

I started out 3 years ago with miracle gro...I mixed it in a 3 to 2 to 1 ratio as 3 parts miracle gro, 2 parts calcium nitrate, and 1 part epsom salts.....no matter what the so called pros tell you, this will grow very nice vegies and plants....the only draw back is that the N in miracle gro, peters, or sam's deep feeding is in the form of ammonia....and urea...these types of N cause the PH to constantly drift down....I corrected using baking soda ...1 teaspoon per 10 gal takes the PH up 1 full point.....I dump the tank at least every 2 weeks and sometimes every week......

OK.....moving on....a few years later....I tried 5-11-26 water soluble hydroponic fert from Southern Ag.....it works fine but the PH constantly drifts up because the N is from nitrates....

I don't like to play with acid....so I now mix 10 to 20% of miracle gro with the commercial stuff from southern Ag.....if the PH goes down to 5.5, I stop using miracle gro....if the PH gets to 6.5, I add a little miracle gro to the mixture.....this works great....my PH runs between 5.5 to 7.5......the plants don't know the difference....try to keep it in the range of 5.5 to 6.5.....

if you read the fine print on miracle gro, peters, or sam's deep feeding, and Southern Ag 5-11-26....they all have about the same ingredients except for the N component......The 5-11-26 also has some epsom salts in it so you can stop using epsom salts or use less......