6.5 is the pH of what? You didn’t say anything about how long between feeding, it seems almost as if you are way over feeding it, but you gave no time schedule.
Yes, you need to learn how to measure the run-off, it isn’t that hard, you just measure the run-off that comes out the bottom of the container. You should get a TDS meter pen, as well as a way to measure pH like strips, drops, or also a digital pH pen.
Also, are you over watering?
Fresh air 24/7? How does this work, where is the “fresh air” coming from?