What should I add?

I have a 22 g tank, heavily stocked with two fan tail goldfish, five head and tail light tetras and one SAE. The tetras and SAE are just temporary visitors over the summer and are going to a much bigger tank in a couple of months.

I maintain a CO2 level of about 30-35ppm (DIY) and have one single plant, a huge watersprite tied onto a branch of a piece of wood. I had been using 60 W for a while but did not see any pearling. Change 30 % of the water once a week. Just prior to the water change the Nitrate was between 5-10 ppm. I have since doubled the light to 120 W and are now enjoying oxygen bubbles forming on the leaves and the goldfish seem much more active in spite of the strong light. The leaves are narrower and smaller compared to when I used 60 W and the Nitrate is now 0ppm. Basically the enourmous and exposed root system of the watersprite is sucking up all the nitrate produced by the goldfish.

Every water change I add about 1/10 of a cup (each cup is 5 ml) of Flourish, a volume comparable to two or three rice grains of potassium sulphate and enough of Aquasonics carbonate hardness generator to maintain a KH of about 7-8.

I assume I should add some NO3. Am I adding too little if the Flourish?

Never thought that I would actually need to add NO3 to an overstocked tank with goldfish.

I do know that the tetras require different temperatures but if you live in warm climate (Perth, Australia) the tank will remain warm throughout the summer. Can't afford a cooler. I think the Chinese cultivated goldfish in large but shallow ponds. In the summer, the water temperature would have been high.

The light is 4x36W CF but is 90 cm long. As my tank is only 75 cm I figured that the lightlevel would be more comparable to 4X30 W. The light sits about 4'' above the cover glass of the tank.