Don't stress out about anything that aquadvisor tells you. It is a software solution from a person who is quite knowledgeable about software but does not seem to be very knowledgeable about fish. I have been on many forums where that particular person has posted a thread and, just like our forum, the people have given him data that may or may not be correct. I am absolutely certain, having spent some time there, that some of the sources he uses for information are terrible. When the resulting calculations say that something is good or bad, I take that as the advice of a single, partially misinformed, person. If you get lucky, the information that you have happens to be the correct information. In my own estimation, a 12 gallons real volume, probably called a 15 gallon, that has your stocking would take a 25% water change weekly to maintain it and if you have significant plantings you could cut that back. Once again, I am a single person whose advice is only as dependable as any single person can be.