First things first, have you checked your water parameters -nitrate, nitrite, ammonia ?
Sounds like the white fluffy stuff is a fungus and the black stuff algae which is probably secondary
to parasites on your fish.
You need to scrape and identify what parasites are on your fish. If this is not possible, a broad spectrum medication like malachite green or methylene blue may help, but one really needs to find the cause of the problem first.
You mentioned you conditioned your water--how did you do this? Also, what medication did you use? it is also very dangerous to use different medications in a short space of time as this can be toxic to the fish and stress it. Hopefully you have a dealer or hobbyist to guide you in your area. The most important advice I can give you, is to identify the problem first. You also need to work out the litreage of your pond.
On your second problem, a net is the best to keep birds out.
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