Thank you for contacting Ask Extension. These are fungus gnats and they can usually be eradicated if you are consistent. There is no sprays that work on all plants to get rid of them. But you can use Bti, which is Bacillus thuringiensis israelensis, usually found at garden centers. 

But that said, they usually occur when plants are top watered. The Gnats will lay eggs and the larva stays on top of the damp soil. If you treat/trap the adults and treat the larva, you can usually get it contained within a couple of weeks. Start watering your plants from the bottom, and let the top 1" of soil dry out completely. Put in yellow fungus gnat traps that can be purchased at most garden stores. The traps will contain the adults, while the drying out of the soil will begin killing off the larva. You can also use the Bti to help kill the larva, but it will work faster if you allow the soil to dry out. 

Here are some references to help you in how to do this. If we can be of further assistance, contact us.

https://extension.psu.edu/fungus-gnats-in-indoor-plants

https://ipm.ucanr.edu/home-and-landscape/fungus-gnats/#gsc.tab=0

Hello,

If you are talking about the Bt being expensive, you can find it at Bordines or any garden store. Same with the yellow fungus gnat traps. Or you can make  your own. Go online and google how to make your own sticky traps, using a plastic material and Tanglefoot, a Insect barrier adhesive. 

I do not know of any globe waters that actually work. Not sure why you cannot bottom water? If it is in a pot with a drainage tray, just sit them in a tub or container and let the water soak up from the bottom. 

If you cannot do that. Then I would push the plants to not water them for maybe 5-6 days longer. That way the soil on top will dry out.

Good Luck!

Yes you can. Read the instructions on the label for hydroponic gardening. You might want to use the Mosquito Dunks for that, though. The Dunks have the Bt in them also.

Usually the BT, since it it a natural bacteria, will only survive in water for a few days, sometimes up to a week. It will depend on  the conditions for temperature and sunlight, so too much heat and sunlight, the shorter the Bt's life.