No Light For 3 Weeks, Now Platy Has White Patch

[FishNChimps]

The light unit died, so I ordered a new one from Amazon which took 3 weeks to arrive. My aquarium denizens were not in complete darkness, being in a living room, but got no natural light. Now the new light unit has arrived and I see one of my platties has a white patch above an eye (in pic). Is this something light deprivation can cause?

I have also been gradually reducing pH over several months by diluting tap water with LFS RO water. It's gone from 8.3 to 7.7, but I've been careful to keep the changes gradual.

 

[Byron]

The photo did not appear, so can't offer much on the white spot.  But on the water parameters, why are you lowering the hardness and pH?  Platy are livebearers, and all livebearers need moderately hard or harder water, with a basic (above 7) pH.  Do you know the GH (general hardness)?  Diluting tap water with "pure" water like RO will lower the GH as well as the pH.
 
Byron.