ITs good for the pH to fluctuatate. The harsher you are on the plant without damaging it the stronger it becomes.
People forget that rain is quite volatile and can be very acidic. Even long time established garden fluctuate every year.
What kind of water are you starting with ?
We started with city water. But found out that it is naturally basic. Had to add pH down from the get-go. Not to mention the relative salts and CHLORINE.
If you want you can jar some water and take it to your local swimming pool store and they will test the water sample for free!! IT will tell you how much salts/chlorine is in there(so they can sell you shit for your pool or a new pool). I would also take 2 samples. One hot water and one cold water, from the tap you plan to feed from. Then average the 2 numbers. Hot water picks up more salts as it flows down the pipes.
We switched to distilled water, its only 90 cents a gallon and pure with a PERFECTLY neutral pH. I am only blooming in a 10 gal ebb so i can rationalize 20$ a month for water.
If you are doing volume, stick to city, buy a ppm meter and a shit ton of ph down cause you will absolutely need both. Also, let the water bubble with an air pump or the water pump for a day to dechlorinate it. The chlorine is a gas trapped in the water and eventually escapes after pulled from the faucet but takes time.
Peace out yo