Use this strength every time you water your plants, but once a month use plain water to flush out accumulated salts. Periodically examine the root system by carefully removing the plant from its pot. If the root ball is very tight and overgrown, it's time to repot into the next size pot. Growing medium must be loose and porous to retain moisture, yet provide good drainage. Use any of the prepared African Violet mixes, with some perlite mixed in to lighten the soil.
Some growers use custom soil mixes which they have prepared themselves.
These mixes may be more compatible with their particular growing environment and watering habits. It is very easy to propagate gesneriads. Most gesneriads can be grown from seed, but many modern hybrids will not reproduce true from seed. Read this description of the gesneriad classification used in flower shows. Here are some detailed propagation suggestions.