Recycling Idea: Use Freshwater Aquarium Tank Water as Fertilizer

fishtank 225x300 Recycling Idea: Use Freshwater Aquarium Tank Water as FertilizerSometimes when we become used to a chore, we stop thinking about what exactly we are doing, and just focus on getting through with it.  I was doing this a few years ago with my large office fish tank, when I was mid chore, dumping gallons of slimy fish water over a sidewalk, and suddenly wondered “what in the world am I doing?”

I keep a very large goldfish tank in my office at work, somewhere in the ballpark of 70-80 gallons.  Once upon a time, the tank was the overwintering and emergency tank for the pond goldfish on my corporate property. It’s been a resort, and temporary home for Comet goldfish for years, used when the fishes ponds were either drained, or undergoing repairs. Being a practical sort of person, in recent years, I’ve been keeping a few fish in there year round as my living screen saver, to keep the tank ready at all times for any Biblical-scale water feature disasters. While I have devised clever ways to cheat the system, and prolong the time between tank cleanings, I inevitably spend an hour twice a month sucking filthy brown water into a tall office trashcan for dumping out on the lawn, or down a drain.

A few years ago I was going through my bi-monthly fish tank cleaning process, wheeling the waste-water trashcan out to the exterior door, when I really looked into the filthy water, and realized that what I was staring at was free liquid fertilizer – and a fertilizer I was about to dump indiscriminately on the nearest patch of land near the door! Feeling like a total bonehead for never having thought about the uses for this “grey water” source before, I began that day using fish water as both a water source, and a fertilizer for my office plants, and exterior potted plants.  A fish’s excrement, and the general waste that they sluff off, are excellent fertilizers for plant life, because they contain so many undigested and beneficial nutrients.

Whether you use a gravel vacuum Recycling Idea: Use Freshwater Aquarium Tank Water as Fertilizer and a bucket, or a long extension vacuum, to transfer recyclable water directly to plants, recycling “gray water,” is a great way to cut down on your total water consumption, using water that has been lightly used for one purpose again for a second purpose before disposal.  Fish water, while unsafe to recycle for any human benefit, will greatly assist your yard, or office plants, feeding and watering them at the same time, and reducing your need for more commercial forms of plant food.  If you own a freshwater aquarium in either your home, or your office, try saving the water you drain from your tank for your own plants, as a way to “go green” this month! Plus as an added bonus, vacuuming your freshwater fish tank in one area and using the exact same water for your plants is a more efficient way of conquering two chores at once!

TIP: For small tabletop fish tanks in the home or office, keep a large watering can available, and drain aquarium water directly into the can for easy dispensing in your flower pots and garden beds!

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  1. What a good idea!

  2. fred@opc says:

    Fantastic tip. Perhaps we should be using our water pump to pump the water out to the yard instead of our gravel vac. Now, if I only cleaned the aquarium as often as I should… sigh.

  3. admin says:

    Mother Nature,


  4. admin says:


    Well, the extra dirty water won’t hurt your plants, that’s for sure, so at least you can assuage any guilt on that front! Happy cleaning!

  5. Elisa says:

    Without any research, I started doing this and my plants flourished! I just found this site. Man, it works! It’s better than Miracle Gro cuz it’s natural and resourceful.

  6. Amy says:

    Great minds think alike! It’s a great thing when a hobby like fish keeping can reap you added benefits isn’t it.

  7. Rebekah says:

    i have a fish tank and told my dad that the water could be used as fertilizer. our garden is right by our well and he’s worried that it will get in there and be harmful. i told him he’s crazy. does anyone know exactly what type of nutrients are in the water so i can back up my info?

  8. B Forde says:

    Rebekah, there are possibly two issues…. chemical treatments you use in your fish tank (eg copper) and the possibility of diseases that might be able to jump species in the water (eg TB). In most cases these would be extremely unlikely to pose a problem to your well water but if i were you i would avoid using the water near the well just to be safe (as an aside people have been sucking up aquarium water through a hose and some of it goes into their mouths for years – during water changes). Most of what is in the water is just ammonia, nitrates, organic substances, harmless bacteria and trace elements.

  9. Graz says:

    Fantastic idea! Just be careful if putting the water near a well, stream or any other freshwater source.

  10. S,kanchana says:

    Need a aquarium cleaner.

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