The curling of the leaf tips is Mg deficiency. This often happens with bottled, R/O, very soft or distilled water. To cure it, get some Epsom Salts and a teaspoon per gal added when you water.
The yellowing & dying leaves could easily be due to low light issues. If the plant is getting no benefit from them and they are not photosynthesising, the plant will let them die. Pull them off (they should fall off easily)
MG soil is not good for MJ. When buying soil, go for something that is NOT pre-nuted (why would you buy soil that has nutrients formulated for flowers like roses or carnations in it? MAD) And if you see "moisture control" on the packet, leave it on the shelf. There are plenty of inexpensive nutrients out there and topsoil is MUCH cheaper than pre-nuted garbage so buy topsoil.
If you only have a small area, mylar from your local growsop will be cheaper than a camping blanket. Better still, if you have flat white paint, use that, it is more reflective than most people think.
Peace W