It possibly can help in some ways as I read at http://www.newton.dep.anl.gov/askasc...1/gen01354.htm
But since you also feed your fish, their poo will be a good source of nutrients as well.
BTW - after watering my household plants with fish tank water, they grow lushier too. This is because aquatic plants needs more nurients than land plants, so the water in our planted tanks have more nurients for the land plants.
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