Nitrites in and of themselves aren't harmful to most of your tank residents, but their presence is indicative of something that's gone a little awry.
Initially, that may begun with an ammonia spike which could have stressed everybody out.. If NH4 now tests as 0, we're past that hurdle so don't worry about it.
That nitrite will also end up as nitrate in short order, which isn't necessarily "harmful" to a lot of things in the tank (though nitrate toxicity seems pretty hotly debated by the chem nerds.. Suffice it to say that high nitrates shouldn't be a reason for you to stress your whole tank by doing a massive water change by adding insufficiently-dissolved salt). But that ultimately ends up as a nutrient increase.
I've seen a few scientific types saying that algaes will preferentially take up nitrogen higher up the nitrogen cycle - that is, they will more readily consume ammonia than nitrite, nitrite than nitrate. Either way, and at some point, something's going to be eating that stuff up and it'll probably look ugly.
If it were me, I'd probably mix up 10-15 gallons of new seawater and change 10% a day until you've used up all the new water. That won't equal a complete water change by any means (0.9^10 = 34% of your initial dissolved gunk remaining, if my math is right), but it'll be much more gentle.
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