@Sophie Nguyen To get more precise ratios of fungi to bacteria (F:B) takes a tool like a microbiometer. You can’t use a microscope to “count” a true ratio. That said, the visual assessment from a microscope tells you a lot about the broader context and the overall presence or lack of fungi, nematodes, protozoa, and more. If you’re going to get a microscope, which is a commitment, then 400x is the closest magnification you need. Anything more magnified is losing resolution. You can also get microscope review from others to not commit that large a purchase. If you are going to, I can get you in touch with people who have good advice for what to purchase.