My guess would be the duck as well. Otherwise, it is one of the younger layers. You say Tetra Browns...but if you got them from the feed store, likely one of those is an Easter Egger rather than a TB. Many feed stores mix up their bins by accident. Tractor Supply seems to be especially adept at...
You can actually take any red based rooster and breed it over any silver based hen and get sex linking for the first generation due to the color genetics along the Z strand.
You can also do that with barring...a barred hen bred to a non-barred (red is often used) will get you barred boys and...
Australorp (black? as is typical) rooster bred over red sex links will get you "mutts" that lay brown eggs well and likely colored black, both genders.
If your rooster is white, likely all chicks will be mostly white with red bleed through.
If your rooster is blue, you will get black 50% and...