Agree. Flourish Comprehensive Supplement for the Planted Aquarium is, as the name indicates, a supplement; i.e., intended to supplement the nutrients naturally occurring from fish food and water changes. This implies a low-tech or natural method planted tank, where we have some plants but the main focus is the fish. This method requires considerably less nutrient quantity than would a high-tech planted aquatic garden method where plants are the focus and fish often do not even figure in the aquascape.
The second thing is that light intensity drives photosynthesis, which means the light determines how much additional nutrients need to be added. This depends upon the plant species and numbers, as well as the extent of natural nutrients from fish foods. Tom Barr has written that once we have the light for the tank, we then add nutrients minimally and observe the plants' response; if more are required, up the nutrients a bit and monitor, to the point where we have sufficient for the needs of the plants but not excess which will only feed algae.
I have fairly well-stocked tanks, though I feed the fish sparingly. I also have zero GH in my water which means no calcium and magnesium, so ensuring sufficient of these is important. I've fiddled with Flourish Comprehensive doses over the past decade, and at present I find one dose at the level recommended on the label just once (not twice) a week is sufficient. I could probably do with less but all of my tanks have a full cover of floating plants as well as lower plants; I can use substrate tabs for the larger planted swords, but floaters being rapid growing plants need a good supply of nutrients and I have worked it out to one dose weekly. This I add on the day following the water change. The calcium/magnesium needs appear to be covered doing this, and that means I do not have to increase the GH which would likely affect my wild caught very soft water fish.
My only real argument with Flourish Comprehensive is that it does contain nitrate and phosphorus. Seachem's web site says, "Does not contain significant levels of nitrogen or phosphorus." These two nutrients are never really necessary in a natural method planted tank that has fish. Plants do not use nitrate anyway, unless there is insufficient ammonia/ammonium in balance with the light and other nutrients, and a deficiency of ammonia/ammonium is extremely unlikely in such a set-up. And there is more than adequate phosphorus (phosphate) in fish foods to supply the needs of the plants in such a system.
