What is this?

What Miss_greenthumbs_Garden said, you need to give the plant a proper flush and move it to a bigger pot, you'll see once you transplant it how restricted the roots already are in that small pot.

Also she looks like she would like a bigger pot x

The yellow or brown leaf tips are caused by too-high levels of nutrients at the roots( so a build up ) which disrupts the flow of water through the plant and causes the symptom of burnt tips on leaves. So I'd recommend giving her a good flush with some pH water and leaving her to dry out and going from there x

generally i would not worry, but : to me it looks like oferfed plant, higher leaves are a bit too dark. Too much Nitrogen. Pot a bit too small, maybe transplant ??? Reduce feeding !!!! give something for roots and Nitrogen uptake. I used Ecothrive Biosys in such cases.