More plants is always good. Ā As far as "fasting" fry, it generally isn't recommended. Ā BUT, with that said, I've been fasting my tank regularly, and I've had several corydoras fry grow up in my tank with NO intervention from me. Ā The live plants actually are home to a variety of microorganisms that normally would feed the fry in the wild, things like "infusoria" and the like. Ā I have a fairly good number of real plants and the fry do just fine without any special treatment from me.
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A 20% PWC won't do much to lower high levels of any contaminant in the tank. Ā Imagine you have 100ppm nitrate, a 20% water change (with 0ppm nitrate tap water) would only lower the levels to 80ppm. Ā Not noticeable on the API test kit. Ā On the other hand, doing a 50% PWC would lower the levels to 50ppm, and a 75% PWC would drop it to 25ppm. Ā Personally, I am a fan of LARGE water changes. Ā The 20% water change schedule that is so often discussed is best for lowly stocked tanks. Ā More heavily stocked tanks really benefit from a much more aggressive water change schedule. Ā I do 25% weekly, a 50% monthly, and a 75% every 6 months. Ā In the summer I do even MORE water changes than that, and do a 25% water change twice a week, sometimes 3 times a week. Ā I use this water for my flowers in the summer, and I use it to emulate a "rainy" season for the fish. Ā It works for me, and I think the fish actually appreciate the change in seasons like this.