I would like to share with you the results of my three-months experiment with real consumption of nutrients in planted aquarium. I weighed the plant biomass (live weight) which were produced in my aquarium regularly (after each trimming). Every time I did some trimming in my tank, I thoroughly shook the water down from plants and weighed it on a digital scale with an accuracy of 0.01 g. This way I monitored the biomass gains for 3 months, and finally I calculated the average weekly biomass gain: 12 grams of live weight for the area of about 35x35cm (60L). So each week approximately 12 g of plants grew up on an area of 35x35cm. Since this is a "live weight", in terms of dry matter that makes about 10% = 1.2 g of dry weight. And since we know that there is about 45% carbon (C), 2% nitrogen (N), 1% potassium (K), 0.2% phosphorus (P), and 0.02% iron (Fe) in plants' dry matter, it's relatively easy to calculate the actual amount of nutrients that plants needed for 12 grams of biomass per week: 2 g CO2, 1.8 mg/L NO3, 0.1 mg/L PO4, 0.2 mg/L K, and 0.004 mg/L Fe. I will add that in my aquarium, I use quite strong light (100-120 µmol PAR at the bottom), nutrient-rich substrate ADA Aqua Soil, I supply about 4.7 g of CO2 per day, fertilize as needed, and each week I change 50% of water. Details of the aquarium can be seen in my presentation (Nano 4). I will definitely continue doing similar tests (and perhaps some other users will join me to have more data from different tanks), but even so, I'd say that I came to quite interesting findings => that even a relatively densely planted aquarium with strong lighting and plenty of nutrients does not need weekly more than 2 mg/L NO3, 0.1 mg/L PO4, 0.2 mg/L K, 0.005 mg/L Fe. Moreover, from the weekly dose of CO2 that I'm adding into my tank (4.7g x 7days = 33 g), the plants actually consume only 1/16. Compare this with the amount of nutrients you supply weekly in the aquarium using different commercial fertilizers, if you stick to the recommended dosage: ADA = 1 mg/L NO3, 0.5 mg/L PO4, 25 mg/L K, 0.05 mg/L Fe Easy-Life = 2 mg/L NO3, 0.1 mg/L PO4, 5 mg/L K, 0.2 to 0.5 mg/L Fe Tropica = 6 mg/L NO3, 0.3 mg/L PO4, 1 mg/L K, 0.07 mg/L Fe PMDD = 1-5 mg/L NO3, from 0.1 to 0.3 mg/L PO4, 3 mg/L K, 0.1 mg/L Fe EI = 30 mg/L NO3 (= 15-times more), 3 mg/L PO4 (30-times more), 10 to 20 mg/L K (50-100-times more), 0.5 mg/L Fe (100-times more) PS: The above test doesn't take into account the increase in root biomass (only partially), which means that the actual nutrient consumption will be slightly higher. Some nutrients in the aquarium will be produced naturally in mineralization (conversion of organic matter into minerals) or may be present in the substrate, which means that the plants may get by with a smaller amount of added nutrients. On the other hand, the efficiency of nutrient distribution will certainly play some role also, as this efficiency will never be 100%, so for this reason it can be wise to use little more nutrients. Also, it's quite a known fact that the amount of phosphates have a huge influence on plant growth. When I limited phosphates in my fertilizing regime, my plants grew very slowly (perhaps only 5 g body weight per week) even under very strong light. But once I increased the concentration of phosphates to 2-3 mg/L PO4, the weekly gains increased to 25-30 g of live weight. My point is not to save some small amout of fertilizer, but rather to understand what amount of nutrients our plants really need, which in turn will help us to understand the usefulness or uselessness of some methods of fertilization. A lot of people grop in what fertilizing method (ie. which fertilizer) to use. As I stated above, different fertilizers have different composition of nutrients. If we know how many nutrients plants can consume under certain conditions (strong vs. weak light, lot vs. little PO4, lot vs. little CO2, etc.), we will know quite precisely what is appropriate dosage. As I demostrated on the example of my aquarium (strong lighting, lots of CO2), my plants will get by even with an extra-poor fertilizer like ADA, which still contains enough of everything, except nitrates, because the ADA relies on the fact that nitrogen compounds are already present in great numbers in ADA substrate (+ something is being produced in aquarium from fish). Virtually all fertilizers (except EI) use relatively moderate concentrations of nutrients ... but these levels are still several times higher than our tank will in most cases need. So although I would use Tropica fertilizer in my aquarium, still the plants there will have a galore of nutrients (= practically non-limiting amounts). EI method in this regard is completely "overstated" because it uses 15-times higher amounts of nitrates, 30-times more phosphates, ~100-times more potassium, and 100-times more iron ... than my plants need. As I said, with large quantities of phosphates the plants will grow faster, but is it desirable? I know no one (except the people who make a living selling plants), who would want each week throw away a bucket of plants. So my conclusion: Methods like EI and PPS-Pro are designed more for the avid plant growers; in normal plant aquarium I would probably not recommend them to anyone (although I was formerly rather their advocate). And the argument that excess nutrients has no effect on algae, I do not consider valid. It's certainly reasonable to use a little more of fertilizer than is the "real" consumption, because the effectiveness of its distribution is certainly not 100% (due to imperfect flow; part of the micronutrients deteriorate before it gets to the plants, different plants have different demands, etc.), but how much more ... 2- to 3-times more? Definitely it's not necessary to use 100-times more. I know that many EI advocates will argue that larger amounts of nutrients don't pose any risk (although I don't think so). Still, it can be useful to know what's the real nutrient consumption in our tanks.