Adding salt until your pasta water is “salty like the sea” is a common practice, but no one talks about the other briny, oceanic flavours the large body of water has to offer. I wouldn’t boil my pasta in actual sea water, but you can impart a bit of minerality and mushroom-like umami with the help of seaweed.
You could do this with any seaweed you like, but I favour kombu (most frequently used to make dashi), which is absolutely riddled with powdery-white glutamic salt crystals (aka “half of MSG”).
In terms of measurements, you can play pretty fast and loose here. I added two 3cm x 10cm pieces to two quarts of salted cooking water, brought the water to a boil, then removed the kombu just before adding the pasta, but you could probably add an extra sheet if you were so inclined.
The ocean-esque water gave the spaghetti strands (which were destined for cacio e pepe) a savoury, brackish note. They were fantastic with butter and cheese, but I think they’d really shine with a scampi or some scallops (duh).
Would it be weird with a red sauce? Probably not, though it might be hard to taste the seaweed. Extra glutamate in your pasta water is never a bad thing, but an acid-heavy tomato-based sauce could obscure kombu’s more delicate mushroomy flavours.
But,if starchy pasta water is a primary component of your sauce, seaweed-boosted pasta water will make your sauce — and your noodles — that much more flavourful.