Rusty circular discoloration on seedlings

So i have about 3 different strains of subcool seedlings going right now, 4 out of my 5 jack the ripper seem to be showing rusty circular discoloration in the center of their leaves however the 5th one looks incredible and my agent orange and plushberry seedlings are showing no signs of this, theyve all been fed the same and kept under the same light so im a bit puzzled
 

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