Older fan leaves dying

Hey team,

My 6 plants are bout 6 weeks old. For a few weeks now my older fan leaves just turn yellow and fall off. It sucks, they don't get any longer than about an inch n a bit before falling off. New growth is perfect but all my old leaves are dying!
Getting some red stems as well.

I just bought a digital pH tester a couple days ago and my tap water is about 7.2 so i've been reducing the pH of the water - but its too soon to see any results obviously.
Also, anyone know if watering with balanced pH water changes the pH of the soil/



Thanks in advance!

Old leaves die from using the food that's in the leaves....Depending on age of your plant....Feed it some nutes..... Get yourself a PPM meter also....