It might be better just to sacrifice specific spots rather than to try to spread it evenly.
Or we could have a premix station where we pump in sea water and mix it with brine at a certain ratio and then return that to the sea.
And with your second process, you still end up with a higher concentration of salt / brine around where it's returned to the sea, still killing animals.
I'm thinking of pumping the brine onto large evaporation lakes and harvest the salt or whatever - which also already happens to produce sea salt.
And if there's too much salt for the market, just stockpile it. Like underground salt mines.