I was thinking more on the lines of nutrient burn and over-watering...
I've found this piece and it mentions the spots, not just the tell tale signs of the leaf tips. ;
Leaf Color:
Edges Appear Brown or Burnt
Dark or Purple Leaves
Black or Gray Patches on Leaves
Brown or Dark Spots
Leaf Symptoms:
Upper Leaves / Newer Growth Affected
Lower Leaves / Older Growth Affected
All Leaves Seem Affected
Leaf Edges Appear Burnt
Leaf Tips Appear Burnt
Leaf Tips Die
Spots
Slow Growth
Twisted Growth
Leaves Curl Under
Plant Symptoms:
Weak Stems
Slow Growth
Twisted Growth
Leaves Curl Under
Other Symptoms:
Buds Not Fattening