Why is it when how much i zoom my noise is different?

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when it is 12.5 my noise are rough, when it is 12.6 it just completely smooths out and completely different from what i had put in, but another problem, when i exported it or merged visible layer, the color of the noise is completely different how can i fix this??
look at the zoom number to see the difference of it, hope i could get a solution thank you:((

the picutre with the plae noise color is the one where i merged the layers(same output with the "export as.")