how to get rid of tiny black midges on houseplants?

When watering put a tiny amount of washing liquid in the water - it works for me - but it might also mean you've over watered - check the plants arn't sitting in water.

sopy water worked for me too its sticky>

Crush a clove of garlic into a pint of water, then water the plant.
The insects sound like Scairid fly/fungus gnat ,harmless to you and your plant however the wire like maggots feed on plant roots and a heavy infestation can harm your plants.
Allow your plants to dry out a bit more before watering. Here's how to check. Push a wooden barbeque skewer into the pot down to the roots, leave it in place for 5 minutes. Take it out, if it's dry or nearly dry water.