I recently bought a miracle fruit that is 1.2 years old. For about 3 weeks it was doing great, growing 2 new leaves already. But I recently noticed the lower leaves turning a bit yellow with brown tips.

I thought this was from lack of sun so I moved it closer to my west facing window. the yellowing of the leaves has stopped and they seem to be turning more green. But I fear the sun was too much. The leaves now have burn marks on them.

Tonight I put a bit of fertilizer In the soil. (The leaves were growing rapidly but there seemed to not be enough nutrients).

I keep the plant in a plastic bag all day and night for humidity and open it for fresh air twice a day. The pH of the soil is around 5-5.5 with help of sulfur. The soil is a 47% sphagnum peat moss, 50% perlite, and 3% citrus plant soil mix by volume. I water when the soil gets a bit dry(it is very well draining). The temperature ranges from 65F at night to 82F at day.

What could be causing the the previous problems and how can I fix them.(p.s. sorry for such a long post)

I will post links to pictures in a bit