Rust on leaves

Hard to say 100% without seeing the full diary or feeding schedule, but from the pics I’d lean towards early calmag deficiency. Pretty common in coco around this stage. Rusty edges and spotting like that usually means they’re getting hungry for calcium and magnesium , especially if the runoff isn’t generous yet. Coco tends to strip those out fast. I’d bump in a bit more calmag next feed and make sure you’re watering enough for solid runoff daily. Coco likes staying fed and flushed at the same time. Hope that helps, just my best guess from the pics. They should bounce back quick once they get what they need.