I was referring to the use of KNO3 as the only source of nitrate. You could also use Ca (NO3)2. There is a nutrient mix for hydroponics called Hogland Solution that has equal amounts of Ca(NO3)2 and KNO3. To make Hogland you use 1 molar solutions of KNO3, Ca(NO3)2, MgSO4 and KH2PO4. To make one liter of Hoglands:
5 ml 1M KNO3
5 ml 1M Ca(NO3)2
2 ml 1M MgSO4
1 ml 1M KH2PO4
Add distilled water to bring volume to 1 liter
They use this strength for hydroponics of terrestrial plants. For aquariums, I mix up a Hogland concentrate 5 times as concentrated as above. (I tried a 10X concentrate, but I got a precipitate of calcium phosphate.) Using my 5X concentrate, I add 1 ml per gallon of aquarium water two times a week in thickly planted tanks. Adding at this rate keeps the nitrate level at 1 to 5 ppm depending on how well lit and how thickly planted the tank is. Basically, I monitor nitrate level and add to keep it in the measurable range. I don't worry about measuring other nutrients, and I change water quite infrequently, something like a 50% change every 6 months.
KH2PO4 is preferred over K2HPO4 in Hogland solution because it is a little more acidic and it keeps the pH down around 6 which is preferred.