Rob i also think you should lessen the water changes.
I have had my nano up for almost a year now.
Its a 5.5 gallon with a false wall, 2x9watt PCs, and biowheel filter.
I do like 30% water changes every month and everything has been fine.
I currently have a snowflake eel, 2 stripe damsels, and a clownfish in there all living strong.