Hi all,
If your tank is planted the level of nitrate will go both up and down (if it is un-planted it will usually rise over time, unless you do regular water changes). This is also one of the reasons for having planted tanks, it makes them more stable and it is probably the single factor that most improves water quality.
Plants will take up nitrogen (initially the ammonia (NH3 or NH4+), then nitrite (NO2-) and nitrate (NO3-), and incorporate it into the proteins within the growing plant. When you prune your plants you remove that nitrogen from the system.
Increasing the amount of carbon available to the plant (e.g. via CO2 addition) or the amount of light energy (more intense lighting) will drive up potential plant growth, and the plants demand for nitrogen (and all the other macro & micro nutrients).
Plants have a high requirement for nitrogen (N), Potassium (K) and, to a lesser extent, phosphorus (P), these are the so called "macro-nutrients".
All the other elements essential for growth (Mg, Ca, Fe etc.) are needed in lesser amounts (these are the micro-nutrients or trace elements)
There is evidence that high levels (~ 60ppm) of NO3 do not effect fish health on their own, but unless you add N, they would normally indicate that there has been a spike in the ammonia conc. of the tank. Ammonia is a by-product of the bioload, from fish excretion, decomposition etc.
If your nitrate level remain low, you may find that plants begin to become pale green and grow less healthily, this is nitrogen deficiency and you can rectify it by adding KNO3 (potassium nitrate). The system of "Estimative Index" was developed for high tech. planted tanks, where nutrients are always available (you add all the macro & micro-nutrients every week) and plant growth is maximised. In this case the system is "re-set" by regular pruning and a large (>50%) water change every week.
Have a look here for the details <
http://www.theplantedtank.co.uk/>.
Personally I don't worry about low nutrient levels, in fact I practise nutrient depletion, the aim of this is to keep the conductivity and nutrient levels in the water as low as possible whilst allowing slow growing plants to grow. The only testing I do is an occasional dip with the conductivity meter.
I wouldn't go down the added carbon route at all, as both CO2 and glutaraldehyde (the active ingredient of Excel etc.) are potentially harmful to your livestock, and for more carbon to have an effect you need to add more nutrients etc.
I'm not interested in maximising plant growth, I like stability and high quality water, there is just much less that can go wrong.
cheers Darrel
