Recycling 20% fish aquarium water changes for use with seedlings or houseplants?

Question

I swear that I have read this information somewhere before, but for the life of me, I haven't been able to conduct a productive web search so as to locate that information again. Does anyone either remember a link or have some personal information about recycling aquarium water for plants? If I am remembering correctly, the low levels of NH4 in the aquarium water provides plants with a easy routine liquid fertilizer, and besides...if I can use the water for something beneficial, why would I want to waste it, by flushing it down the toilet?

Answer 1

From an environmental chemistry perspective, this idea makes perfect sense.  Adding fish food to a tank adds nitrogen, carbon, etc. to your tank water, and of course the fish excrete this as urea, undigested carbonaceous material, etc.  Bacteria convert urea to NH4, then nitrite, then nitrate.  All these forms of nitrogen are fine fertilizer for plants.  

Unless you have a lot of fish in a tank, you are not likely to get enough nitrogen in aquarium water to do a lot of fertilizing for plants.  Still this is a fine form or recycling.  The aquarium water is easier on your plants than (chlorinated?) tap water.  Removing 20% of aquarium water 2-3 times per month is a good practice to prevent buildup of nutrients and other dissolved solids.