Leaf curl under usually means overfertilization. It can also be caused by the following: K deficiency or Copper deficiency. Copper deficiency is rarely seen in indoor plants, therefore rule it out. Most likely overfert.

Older leaves turning yellow is most likely Too much Nitrogen, can also be the start of Magnesium deficiency.

My guess both problems are overfertilization. Hope this helps Gatey-baby.