Eclipse 12 - Amazon sword unhealthy

I just planted an amazon sword in a newly set up eclipse 12 gallon
tank. Within 24 hours some of the leaves turned dark green in spots
and some other leaves turned clear in spots. I also noticed some mild
brownish color on some of the leaves, but I planted it in flourite
substrate and when digging the holes some dust came up so I assume
that the brown is from the flourite dust.

I have three happy tetras in the tank so I assume that the water is
fine, though I haven't been able to test it. What could cause the
amazon sword to start dieing so quickly?

Mike