Regarding your NO3 issue, there are a number of things you could do.....
1. Reduce stocking density (this is a very obvious answer admittedly); AND/OR
2. Install CO2 in order to enhance plant growth. CO2 makes a very substantial difference in terms of plant growth. In my experience plants suchas Echinodorus(Amazon swords) grow slowly without CO2.; AND/OR
3. Surface plants (including Ceratophyllum demersum as a surface plant). The drawback is that surface plant will cut out the light for the plants in the bottom, so they have to be used with care; AND/OR
4. A method apparently used in Asian fish farms, at least according to PFK (I do this in my paludarium, but in a paludarium this is rather easy). This would be to use house plants (such as Pothos- not all house plants are suitable). You would need a cutting with its lower part in the water and all the leaves out of the water. The problem is that this would take space and if the aquarium is filled to the top the plant cannot be fitted in a conventional hood. The growth of some such plants, in the right conditions, can make a significant difference; AND/OR
5. Increase water changes (this however depends on the water changes you are performing now).
You may of course use all these methods or any combination, depending on your specific circumstances.
Joseph