How often should i add plant fertilizer?

Question

i just bought some "Plant Gro" aquatic plant fertilizer, and it says how much to add to my aquarium (2.5 mL) but it does not say how often it needs to be re-added. What is a good way to tell when you need to add more?
Contains:
.15% nitrogen
.0005% boron
.0005% copper
.26% iron
.05% maganese
.0007% molybdenum
.003% zinc

five gallon aquarium, 12 inch 8 watt flourescent light bulb, only two plants- jungle vallisneria and one other one i dont know but it has broad leaves

Answer 1

Because your tank is small and your plants few, use this this stuff carefully or you could find yourself combatting resiliant algae. I would use only a portion of the recommended dosage and add more only after a water change, enough to treat the replaced water.

There is no sure way to tell when you need more - the plant health is a balance between light, water nutrients, and soil nutrients (for rooted plants), as well as available co2. If you find your plants lacking in health or growth, it's best to research the problem and try to narrow it down, rather then randomly add a fertilizer and hope it helps and doesn't cause further problems.

Answer 2

So you think that farmers spend hundreds of dollars per acre for no reason whatsoever??? I can see you know absolutely nothing about agriculture. Look at it this way, considering how the population continually increases in poverty stricken areas of Africa, apparently babies must grow quite well on starvation rations and poor nutrition. I can't see why people in developed countries waste their money providing nutritious diets for their children. Do you think that it may be because with proper nutrition, children grow faster and are more healthy? Plants or kids, it's all the same.