Algae problem in Soil, buying gritty mix / 511 on net
Hi, I changed and re pot Meyer lemon with citrus soil in may which I bought from local plant house. I am giving fertilizer and my plant is looking fine, holding fruit and blooming . But for last couple of weeks It is raining and getting humid and soil has hard time to dry, I noticed there is fine layer of Algae on soil. Just wondering it is bad in short or long term. Soil was low quality ? What is that white mark on stem just above soil ?
I read a lot about gritty mix and 511 here but I can not buy it in Europe. I live in northern Europe and I am wondering which soil type would be good how i can purchase it online ? I noticed these potting mix need fertilizers, which one can buy on amazon or ebay, Right :) ?