Originally Posted by aklick
My nitrates are always at zero. How do I determine if my plants are lacking in nitrates? The only thing I supplement with right now is seachem flourish Complete.
Plants don't need nitrates, unless you are running a high-tech method with high light and diffused CO2. Even then they generally don't need nitrate, but nitrate is a safer form of nitrogen so it is what is commonly added.
Most plants in the aquarium prefer nitrogen in the form of ammonium. Studies have shown that in the presence of both ammonium and nitrate, plants will first take up the ammonium and only turn to nitrate when ammonium is exhausted. And other tests have shown that nitrite is actually preferred over nitrate by the plants tested. But no one is going to dose ammonia or nitrite.
The ammonium comes from ammonia produced by fish respiration and the breakdown of organics in the substrate. In natural or low-tech systems you will not run out of nitrogen. Plants may grow more slowly of course. I have a plant-only tank (no fish) which I run continually since I use it to QT new fish when I get them. The plants do fine in this tank, for months running without fish; they just grow slower.
To the Flourish, there is nitrogen in this, in both ammonium and nitrate forms. But it is minimal, since this nutrient generally occurs naturally in sufficient amounts in a fish tank. Again, talking about natural methods.
I personally would never add nitrate to a fish tank. The effects of nitrate on fish is documented, and while it is not as toxic as ammonia or nitrite, it is nevertheless still toxic.