I looked this up for you.

They are probably fungus gnats, which lay eggs in the compost. So put small pebbles or grit to cover the compost. Make sure the saucers or containers are quite clean too.

If you don't want to add pebbles allow the compost to dry out between waterings, as this kills the larvae. You can also try putting sticky trap cards in each pot to catch them.

yes it is a problem especially if you keep the plants over wet. follow steragrams advice.

Sometimes they can persist, especially in heavy compost, which isn't good for the plants, either. If so, try using a drench of weak tea; or products containing Bacillis thuringiensis israelensis, or beneficial nematodes. Also drench your sink and shower drains with a chlorine bleach solution, since they can also colonize the drains.

Thanks everyone for your answers.

add a clove of garlic to 1 litre water dilution or 1 cigarette to same amount. the garlic can be used in every other watering but the cigarette infrequently.

Or transplant into non-clumping clay type cat litter. that way you cannot overwater the plant. excess water ends up in the drip tray.
you will need to feed the plant more frequently once it has become established in its new home.