How do I get rid of gnats from soil on a house plant?

did you rinse off the soil before re-potting it? Try neem oil

Put fine sand all over the top of the potting soil. Does not have to be deep, but deep enough to cover it all.

I hang a 'No-Pest Strip' on the outside of the flower pot and it kills all flying insects in a matter of hours. I then leave the strip where it is to do its job when/or if any eggs should hatch later.

I forgot to tell you, the No Pest Strips can be purchased at Home Depot.

If it were mine, I would spray Simple Green on the soil. Also spray your sinks and all the drains. Simple Green is safe for the soil on the plant but will kill any flying gnats or fruit flies etc.

First off what are knats?

tiny little flying bugs that live in a house plant soil

Diatomaceous earth (food grade) can also be used.

Don't know why, but a horticulturist told me to do that and it stopped them.

I had a terrible gnat problem and the vinegar traps worked perfectly! Simply place a few tablespoons of apple cider vinegar or white vinegar, a few drops of dish soap, and a tablespoon of sugar in a bowl and stir. Set your bowl in an area where gnats are prevalent, such as near the plant. This took care of my problem in just a couple of days!