Problems first time grower.

The leaves on my plant are turning yellow, curling down slightly and there are some red stems. This is the first time I've grown a plant and initially it was just an experiment with a seed I found, up until this point it was growing outside without any nutrients only water just fine. However since it started flowering I decided to purchase a tent and start using some nutrients and pH balancing the water etc and now I'm having these problems.

need more info to help. what is the medium it's in? what and how much are you feeding it? what kind of light is it under? what is the temperature and humidity?

Like @NanoGadget said. Need more info.

Since it was growing outside, was it in the ground? If it was, did you use the same soil? Added new soil? Was it in the same pot???

Moving a plant from outdoor to indoor is risky on it's own. It's tough to replace the sun and breeze. But off the top of my head, it looks hungry.

Couple of other issues I can think of as well :

1) Sunlight is the ultimate light, and unfortunately that weak blurple one is not going to come even close until they get "used" to it (yield will suffer).

2) You just brought in a scary amount of bugs you cannot see in the dirt etc. So keep a watchful eye.

3)100% agree with needing more info & with Boreal about looking like they need some food.

Good luck!