PH change

[Milton]

Why does the PH jump after about 4 days? First time grower with bubble system

[Toker1]

Ph raises because your plant is absorbing the acidic nutrients from the water. Leaving behind a more basic water mixture.

[Eliot Pryor]

Bet the plant is using what it needs and it changes the ph.

[Tersky]

Plants release a lot of compounds (sugars and starches mainly) into the medium (hydro medium is water) as light is turned into food. This is why res changes are necessary every week or so. Also, the act of agitating water (air stones) causes ph to rise. And finally, like others have shared, the consumption of nutrients in the water changes ph. Why your's is "jumping" could be part or all of those reasons, but if you notice ph fluctuations on a fresh res there could be an issue like root rot, high res temps, algae or pests.

[Toker1]

New plastic will cause ph to fluctuate. Also, temperature changes.