Hard seltzer turns pink after a few weeks, why?

I've got a bit of an odd situation. I've been brewing some hard seltzers, simple recipe: 4LB Dextrose + Champagne Yeast + Water + Nutrient.

However, I've got an odd issue. 2 of 3 hard seltzers have turned a light pink hue after a few weeks in the fermenter. The first time this happened, I figured it was iron in the water perhaps as I didn't use my standard brewing filter. The second time, I filtered the water carefully. Each time all equipment is carefully sanitized.

There is one hit on the internet I found with a similar phenomenon, and although the issue is unresolved in that thread, someone brought up alanine deprivation and suggested extra yeast nutrient. The first time I brewed, I used probably more yeast nutrient than the latter two times and granted it didn't have any pink hue.

However- I can't verify that information. Could lack of yeast nutrient cause a fermented water/sugar mix to turn pink? Is there anything about it that would possibly make it unsafe to consume? Can I counteract the pinkness at this point- or is it too late?