Probably its the ph. One of the most important things in soil 6.0-7.0 coco 5.5-6.5 for example my water from my filter is about 8 which is not good at all!
Okay.. Without any details one cant really offer any decent advice.
Literally no soil, nute, light info or anything.
I can see why ph jumps to your mind
That depends on the medium completely. A lot of potting soils buffer pH for you. I've run tap water from 5.7 to 7.5 plus through soil and never had a pH problem. In fact, my first ever pH issue in soil just happened and it was because I was hammering plants in 1 gallon plants with nutrient solutions and acidified the soil. If your just watering a decent potting mix or super soil pH probably isn't the issue.
If it's coco or peat that's a beast of a different nature, and maintaining proper pH will be extremely important.
Either way, that plant looks hungry for some N. Need more details to know if it's underfed or a pH issue.
Edit: just realized I'm stoned and that was a little unclear. I've never had a pH issue in soil when when just watering.
Okay.. Without any details one cant really offer any decent advice.
Literally no soil, nute, light info or anything.
I can see why ph jumps to your mind