This article is from the Aquaria: Plants FAQ, by multiple authors.
Lack of fertilizer shows up in your plants, as sickly transparent or
yellow leaves, as holes in the leaves, and as reduction in plant
growth. Old leaves die off more quickly than they are supposed to, and
the new leaves are small and stunted. Another symptom is the plants
grow very well for a month or so after you buy them, but then stop as
their internal supply of trace elements and macro nutrients run out.
You also need to add fertilizer if you have high levels of CO2 and
lighting, but no plant growth.
 
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