my chinese elm has red spider mites, but i just need to know how to get rid of them.

You need to use an ornamental insecticide called AVID. It is expensive but it is systemic and will eradicate them long term it stays in the plant for 60 days. It's kind of pricy but depending on how many trees are infected and what value you put on your tree it's the best bet. Other products will work to control mites, but not eliminate them. I have had mites several times over the years and this always does the trick. Make sure and follow the directions to a T and use long sleeve shirt, gloves and safety glasses.

www.domyownpestcontrol.com/avid-015-ec-m...6YmboCFaV7QgodiBkAnA

If you spray with a weak solution of soapy water that will be better than insecticide, also raise the humidity and they will dissappear.

Soapy water is in no way better. Spider Mites have a 3 day cycle. This means if you killed every mite on the plant, in 3 days new ones would hatch from the soil and and reinvest the plant. Avid is systemic and will stay in the plant for 60 days. This means when you spray all the mites will be killed and in 3 days when new ones hatch they will bite into the plant and die immediately thus stoping them from reinvesting the plant. Soapy water is a bandaid that won't last. It's just a cheap way to limp along. Avid is a one time spray, if done correctly.

Then it needs to be done again. It also means that any insect will be killed. Bees etc. Red spider mite are not insects, so it may not be effective.
Raising the humidity will also get rid of them.

No Avid is a one time use, and is designed specifically for spider mites, just read the label on the link. You could spray an infected plant with soapy water every day for a month and eventually the mites will come back. Bees are killed as a result of acres and acres of production crops being sprayed with chemicals, year after year, not because of a couple Bonsai enthusiasts spraying one or two trees a year. You would be more effective at stoping bees deaths by not buying any non organic vegetables at the store than to not use a small amount of insecticide at home.