Hello there,
I Normally get a 50% sugar and 50% salt, and then sprinkle it on the salmon and leave it overnight this will draw out the oil ( for farmed salmon this is always the best way to go).
Of course you can have more salt than sugar or vice versa. I just mix up a batch then pour it over the bottom of the tray and then place salmon in and pour the rest of the salt/sugar mixture over, normally about 5-10mm covering.
Hope that helps[

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Stormdiver