African Violets need to be fertilised regularly and moderately with a balanced and preferably urea-free fertiliser.
I tried several brands and types of fertiliser on my violets, and the one that they liked the most is called Dyna-Gro GROW 7-9-5. I bought it on Trademe, but you can also buy it from here: www.bioleaf.co.nz/dyna-gro/grow-liquid-plant-food . I’m not affiliated with the company that sells it, but this really is a great product so I’m happy to recommend it.
I generally use only 8 or 9 drops per liter of water, as most of my violets are on wick watering (with constant supply of fertiliser, the concentration needs to be lower).
While fertilising violets is essential for healthy growth and blooming, overfertilising will not make violets grow better. Fertiliser burn is a serious problem that will happen if you get too generous with violet food.