How can I deal with corrosion from saltpeter (salt from the ocean) on my desktop computer?

So first of all, I'm fairly certain the salt in the ocean is not niter. Saltpeter makes a very good fertilizer, whereas the salt in seawater kills plants. I'm like 95% sure it's sodium chloride. Anyway, that's not super important here, since A: both salts increase conductivity of water, leading to corrosion, therefore the difference is unimportant, and B: more importantly, salt from the ocean does not evaporate with the water, so salt is actually not a factor.

It's true that corrosion is more of an issue when you live near the ocean, but it's not the salt in the water that's the cause of the problem. Unless your computer is IN the ocean, it's not going to have any issues with salt, only humidity. Humidity is a problem. If water condenses inside electronics it can cause corrosion and short circuits. Boats have issues with salt water being corrosive, so they use galvanic protection and a sacrificial anode to ensure the anode corrodes instead of the hull. This is only possible in a liquid though, since the air contains no salt and is not conductive enough to form a battery.

There are a few treatments you can apply to circuitry, though they're oily and gross, and I do not recommend them as they can cause issues with plastics. There are anti-oxidation compounds like DeoxIT, or water displacement compounds like WD-40, though neither of them are recommended for electronics. I've used a compound called ACF-50 before, which is supposedly designed for this sort of thing. I dunked a motherboard in it for use in an outdoor signage display. It lasted four years in a fairly hostile outdoor environment, so I can vouch for its effectiveness. It was however, quite expensive, smelly, and messy. The computer will drip purple liquid for a while.

The other approach is to dehumidify the environment. Air conditioning does this as a side-effect, but you can also get dehumidifiers that would consume less energy. I suppose one last option would be to somehow heat the computer so that it's always hotter than room temperature, so water won't condense on it, which is a silly idea, unless you happen to have a hot water radiator in your room you could sit it on top of, but then, heat shortens the life of electronics too, so yeah, not a great idea either.

Anyway, after all that, my recommendation is to get a dehumidifier if you're concerned. There's not much else you can do really.

Look into "conformal coating". https://uk.farnell.com/Search?storeId=10151&catalogId=15001&categoryName=&selectedCategoryId=&langId=44&categoryIdBox=&st=conformal+coating

Look into sealing the enclosure and then filtering the airflow.

You might want to look at vapour phase inhibitor / vapour phase corrosion inhibitor / volatile corrosion inhibitor. https://en.wikipedia.org/wiki/Volatile_corrosion_inhibitor If you use these you'll have to seal the box and that means you'd need to water-cool it.

I used to build equipment that went down coal mines. Corrosion was a severe problem. Here's a video that includes one of the machines. There's a box with a blue display panel - that's a "Chock Interface Unit": https://youtu.be/WmwEB4DY_jc?t=134 Here's another video that talks about chocks and longwall mining. https://www.youtube.com/watch?v=N8hXAGNfQmU

Sounds crazy, but fully submerging everything in mineral oil should do it. It's non-conductive and excellent at dispersing heat.

To be clear, I'm not saying dip the components in mineral oil temporarily to coat them; I'm saying permanently install the components inside an aquarium where it will live. You can run it fully submerged (minus the connectors). Bonus: add some fake fish and LEDs to complete the build.

https://eleccelerator.com/aquarium-computer/