6.6 gallon green rasbora + amano's

I would say your ok. Stocking is one of those things that is a guideline and several variables will affect what you will consider to be doable. The amount/type of food going into the tank, the plant density and type of plants, substrates, filter media, water changes and others. You could have a single fish and overfeed a lot and have poor water quality. If you want to know how all these things are affecting your water quality then I would suggest a test kit. Guidelines are good but they are not rules nor will they ensure your success. you can successfully keep an overstocked tank with proper feeding and water changes providing the type of fish you keep won't be to stressed from overstocking as some do well and other won't. If you can test you can make the necessary adjustment to feeding and water changes or media. You will also be able to get more detailed advice from the forums as to where your problems may originate and possible solutions.

Dan