11-04-2009, 08:08 PM
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Plants require a balance of 17 nutrients. Some of these may occur in your tap water, some will come from the fish food, but the chance of getting everything in the required amount is unlikely. Dosing individual nutrients is risky at best, and can be dangerous. Some nutrients in excess can lead to deficiencies in other nutrients because they affect the plant's metabolism.
The EI method of dosing quantities of certain nutrients appears to work in aquaria with CO2 and mega light, i.e., high-tech planted tanks; its inventor and proponent, Tom Barr, says as much. In low-tech or natural planted aquaria, this is not a good practice. The light and CO2 will be much lower and to balance 16 nutrients with this is not simple (CO2 is one of the 17 nutrients, as carbon). The best solution is a comprehensive fertilizer.
I have used Seachem's Flourish Comprehensive Supplement for the Planted Aquarium for more than a year now, with very good results. Previously I used Kent Freshwater Plant Supplement, also successful. These are liquid fertilizers, adequate in most situations. But if you have swords or crypts, plants which are largely bog plants in nature which means they absorb largely through their roots, substrate fertilization is beneficial. And swords (Echinodorus species) are heavy feeders. For these I use Nutrafin's Plant-Gro sticks; there is also a tablet in the Flourish line.