I found this on the net somewhere, hope it helps, I use coffee in some of my plants that like acidic soil, but other than that, I do nothing but use fertilizer with trace elements.

pH is short for puissance de hydrogen and refers to the measure of acidity or alkalinity of any substance. A pH below 7.0 is considered acidic, while a pH above 7.0 is alkaline. Correct soil pH is vital for the health and performance of African Violets. Optimum soil pH ranges from 5.8 and 6.2. A good potting soil, which has been blended especially for African Violets, will have the correct pH. However, there are other factors which can affect pH, such as concentrations of fertilizer salts and soft water. If the pH of the potting soil varies too much from 5.8 to 6.2, your African Violet will not be able to absorb the proper amount of nutrients it needs. For instance, high pH can result in a decifiency of iron, whereas low pH can result in a deficiency in phosphorus.

Tahnks for info, but I'd like to know what will happen with phisical condition of AVs (leaves, crow, flower...)
I bought a pH, light, moist. tester (all in one) and checked the pH ....... and it's says that the soil pH 7.0.
Also I checked the water that I use for watering and it's also pH 7.0.

siracuzi, check the link below; Doctor Optimara is a good diagnostic tool and you might want to bookmark it.

Good luck.

Korina

Here is a link that might be useful: pH imbalance