gnome said:
I originally thought that iron would be more important than Ca and Mg
Because most people have hard water or supplement up to a GH of 4ish, hardness issues are rarely a problem. However if you have none, it may well become a large and more significant problem than not enough micro nutrients.
First significant micro nutrient to consider is iron and the rest are usually scattergunned at with broad range micro sources like Flourish. I find TMG offers a broad enough range of micros for my needs even though it is considered by many on these forums to be too narrowly focused. I have yet to observe deficiency problems that lead me to add any more than TMGs recommended .004 - .014ppm iron. I have seen tanks with much more iron added, most notably Eric Leung's, and I have yet to find strong motivation to try major Fe dosing myself.
Naomi gives the simplified heirachial list but she forgot to elaborate on how to use it.
First nutrient to consider is light. This is usually chosen somewhat arbitrarily when one first sets up a planted tank. It may be that an aquarist reads a few posts on this and other forums and decides they need 5 wpg cf illumination or perhaps they buy a tank with a single tube provideing 1wpg or less. Regardless of the decision made in choosing the amount of light, this choice affects all other nutrient factors.
Second factor is CO2. Carbon is the basic building block of life and plants by the miracle of photosythesis use the carbon in CO2 to build. In most contemporary planted tank discussions, particularly those that consider fertilization scheams, the use of CO2 enrichment is considered essential above about 2 wpg. If you are below this break point in lighting and do not use CO2 enrichment then you will not have to worry much about fertilization. A well balanced product like TMG (Tropica Master Grow) will be all the supplementaion you will need; your fish, food and water changes should provide all that is needed.
Now if you do decide to use strong lighting and CO2 enrichment you may well use up all the nutrients provided by your fish and need additional fertilization to to get the lush growth seen in photos.
The first and most significant macro is Nitrogen, usually dosed as pottasium nitrate (KNO3) often called stump remover. Your fish give off a lot of N as a byproduct of breathing in water and excrement. A tank with lots of N is often very green and has big full leaves. One nice thing about KNO3 is that it also provides K or potasium and when used in conjunction with a P (phosphate) source produces a nice ratio of three growth nutrients.
If you have found the estimative index on line you will find it recomends a 10/1ppm N/P ratio. In my own experience, I prefer a 8.25/1ppm N/P ratio and that is easily measured by 1/2 tsp KNO3 to 1/4 tsp enema solution (one common P source). Depending on your feeding methods this ratio will change. Often tanks fed live foods need less P while tanks fed prepared fishfoods, formulated to be low in P, may find a need for more P in their ratio. I think that 1/2 tsp of KNO3 will produce about 10ppm N in a 30 gal tank and currently I supplement 1/2 tsp in a healthy 60g tank every other day.
I'm sure I missed some points... but have tired of typing. Perhaps others have more to add.
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Jeff