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Using Aquarium water for house plants

April 27, 2006

When doing water changes in an aquarium, I've started using the water that I was removing to water the plants in order to avoid wasting it. I did this under the assumption that the water would be harmless and even perhaps beneficial to the plants since it would contain waste from the fish that may be utilized as fertilizer. Is the correct??


Comments (31)

  • uninformed_kitty

    Aquatic plants eat nitrates, so it stands to reason that land plants might, too. So long as you're not putting anything in the water to kill algae or something, it should be fine. (Do they make such a thing?)

  • littlehippygirl

    Old aquarium water is fantastic for plants, especially if you have fish that create a lot of waste like goldfish. The only thing you have to watch for is to avoid watering house plants with fish water if you've added any of these to the tank: aquarium salt (or any), any medication, or any chemical, including pH adjusters or algae killers etc. The last two generally aren't safe for aquariums anyway. pH up is fine if you know exactly what you are doing, but pH down (acid) and algae ridding chemicals (pesticides) are generally more harmful than good, for both your fish and houseplants.

  • anton_grower

    There is nothing better that i can use for my plants. I grow potted fruit trees like various citrus trees, blueberries, rasberries, persimmons, figs...and i water them all with fish tank water thats rich in fish waste. I even water my baby citrus seedlings and they're doing awesome. Of course, i have never added any chemicals or salt in my fish tanks so that i can safely use the water for my planted indoor/outdoor beauties. Anton

  • garyfla_gw

    i use aquarium water exclusively for my orchids except for natural rainfall. Don't know how effective it is as a fertilizer as obviously if it were too strong the fish would be dead lol. Certainly falls under that old standby "Weakly weekly".
    Many types of plants will root quite readily in aquarium water. take a piece of cork or styrofoam put a cutting through a hole and float it in the tank. The success rate is about three time plain water.

  • littlehippygirl

    Oh that's a neat little tip for rooting :)

  • utsharpie

    the reason they root better in aquariums is because most aquariums have an airstone or powerheadfilter to oxygenate the water.

    cuttings need water and lots of O2 to root.

  • PhoenixRain

    My plants grow and look much much better when I give them a much needed drink of fishtank water. I have never had a prob using it at all on my plants, in fact it helps when I transplant or for establishing a new plant faster. yum yum they say

  • fairy_toadmother

    i do it all the time :)

  • kgrimes

    I have been using my tank water for 6-8 months now and my palnts seem to really benefit from it! I also started watering my new seed with the water and it seems to improve germination somewhat! YAY! Recycling at it's best!

  • bellegallica


    I plan on starting this soon as I've just set up a new aquarium.

    I was wondering, does anyone know what the approximate nutrient analysis would be for aquarium water? You know, in terms of the N-P-K thing?
    I'm not doubting anyone's word about how good it is for plants. Just simple curiosity.


    P.S. I, too, love the idea of floating plant cuttings in the aquarium. Gotta try that!

  • garyfla_gw

    The N-P-K would naturally be relevant to the fish load and how long the tank has been setup.. By the time you tested it would be different again lol. My guess is that it'a about a third of the necessary nutrients for most plants. The great part is that it could never burn and all the elements are in a stable form. Certainly better than straight tap water,but wouldn't expect to quit fertilizing.
    My orchids seem to do well with it and I only resort to chemicals about every two months.
    A lot of tropical plants can be grown permanently with the floating method. Be sure to remove all the soil and keep the leaves out of the water.

  • RPW789_hotmail_com

    I am a high school student, and am doing an independent research project and my topic is to prove if aquatic water does help plants grow. I was just wondering if anyone had any helpful tips/hints. Any info would be great!


  • petiolaris

    Well... some plants benefit from Nitrogen and wasteproducts do have Nitrogen in various forms - NO2, NO3, NH3. In a typical pond you have an ecosystem that is maintained by and with the wasteproducts of plants, animals, aided by bacteria.

  • garyfla_gw

    I suppose the first thing you'd need is some way to test the aquarium water ?? Might check out some hydroponic sites to see what they use. Obviously all the elements would be in very dilute form . What do you think you'd test for?? gary

  • birdwidow

    Since I use sponge filters in all of my tanks and clean them in tank water, by the time I'm done squeezing out the sponges, the water is probably loaded with more nutrients than it had when I siphoned it out, and also contains far more minute solids. As a result, I need to strain it before using it on my smaller potted plants, or the mulm will dry out and build up a crust on the top of the soil.

    Otherwise, it's about the best thing you can do for house, garden or greenhouse plants and as I keep so many Amazon tanks, the slightly acidic water is especially appreciated by my acid loving plants and may be one of the reasons why my gardenia shrub is currently blooming and reblooming in the greenhouse, in the midst of a Chicago winter.

    But I never thought of using the tanks to root cuttings. Great idea! I wonder: as my Amazon fish so love peat water and the jiffy cubes are such a handy means of starting seeds, perhaps I could devise some means of floating a tray of them in one of the larger tanks and get a double benefit.

    Any thoughts on that?

  • petiolaris

    Now you're heading into a different realm of cutivation - carnivorous plants and their need for soil media that is acidic. Hobbyists use a lot of sphagnum peat moss, which is what is in the jiffy peat pellets. Some have used the peat trays to germinate seeds.

  • birdwidow

    petio: I don't have any carnivorous plants and the only acid loving decorative plant I have, other than the evergreens in our foundation planting, is my big gardenia. I knew the jiffy pots are made of compressed peat moss, but was and remain unsure as to how to go about using them in the float-on-tank technique.

    The only thing I can think of for the present, would be to place them in openwork flats, then devise some type of support to prevent them from dropping down below the surface. Or, use aquarim sealant to affix some styrofoam around them, as a means of floatation.

    What do you think?

  • garyfla_gw

    Wouldn't you be concerned with keeping the seeds too moist?? Maybe some types of water plants?? Wouldn't work too well for CP's or Cactus though lol
    Some terrestrials I've grow with roots directly in aquarium watr. Ficus,3 kinds, Calatheas, Marantas african violets as well as several Gesneriads.Spaths and Philos. Trying it on some orchid species .Jewels, and Paphs. Sobralias. and Calanthes. Too soon for the last ones gary
    All the usual marsh plants respond very well. gary

  • hamadrys

    I use a conditionner for my fish : Jungle Start Right. Would it be a no-no to water plants with the old water then. I never did it yet. Thanks

  • birdwidow

    hamadrys: Removing the chemicals and neutralizing any dangerous metals in tap water for the safety of the fish won't make the water any less beneficial for plants after the fish have loaded it with their own nutrient rich waste.

    However, as Gary suggested, you shouldn't abandon plant fertilizer altogether. I may water my gardenia from an Amazon tank, but still feed it with Miracid. Any plant confined to a pot that drains out excess water needs to be fed regularly, so just give yours tank water and see how they respond. If they need more fertilizer, you will know soon enough.

  • ryan_bio

    Thanks for all your help and input! Greatly appreciated!

  • triple_b

    I use a bit of coarse uniodized salt (AKA Pickling salt) in my tank just to keep my tropicals healthy. There is probably 1 tbsp worth in the whole 30 gallons. Would this be harmful to my houseplants? I also have my tomato and various seedling of annual flowers started downstairs. Would it be overwhelming for them to be watered with this?

  • garyfla_gw

    I would say probably not but if it did any harm it would be slow and hard to detect.
    A tbsp in 30 gallons is not doing anything for the fish anyway, So why risk it?? gary

  • triple_b

    so then what IS the recommended amount of salt in a freshwater tropical tank just for health sake of the fish?

  • garyfla_gw

    Have kept tropical and coldwater fish since around 1953 and have never used salt. Have often seen it recommended for various treatments but IMO a plain old water change will work just as good lol.

  • petiolaris

    Salt is reputed to having soothing qualities as well as stimulating slimecoat. So that's what we used at the wholesaler, in conjuction with TC or EM or whatever.

  • remz

    Bit of a bump (felt that extra info wouldn't hurt):

    In response to the aquarium salt question, it is not necessary. It 'can' help with disease and some fish-keepers use it as general maintenance (1tbs per 5 gallons). I wouldn't bother, I've used it a few times for 'aiding in treatment' with no confirmed results. Certainly don't use a 1tbs/5gal mixture of aquarium water to water you plants.

    Most aquatic plants thrive on NitrAte, which is only present in an established (and HEALTHY) aquarium after it has become cycled. Fish waste (Ammonia) is eventually converted to NitrIte after beneficial bacteria has established in the filter. Both are poisonous to fish and some plants help in absorbing these harmful chemicals (java moss to name one). After a bit more time, another type of beneficial bacteria will establish itself in the filter converting NitrIte in NitrAte. Nitrate is what aquarium plants thrive on (as well as most common forms of algae).

    Given this, well established aquariums should ONLY have NitrAte present. As with aquarium plants, house plants tend to thrive off of this nutrient. I can only speak for aquarium plants, but I would suspect that some "easy to care for house plants" would only need aquarium water as a fertilizer if the nitrate levels are at a moderate level.

    As far as backing up the "propagating plants in fish tanks", I've started a few spider plants by floating the roots in my aquarium water with VERY accelerated results. The roots are present within 24 hours and within a couple of days the roots are around 2" long. Plant in soil watch em grow. I water all of my plants with aquarium water.

  • greenhandsprout

    I use aquarium water for my house plants and my vegetable garden during the "Vegative" state I use it every other watering/day my plants grow faster, bigger and beautiful they love the nitrates/nitrites and good old nitrogen, Once your plants are ready to "Flower" or "bare fruit" I cut out the Aquarium water because a "flowering" plant requires more Phosphates and much less nitrates. If you adapt this to your personel growing needs you'll be rewarded with beautiful plants of all kinds. Remember the Dirtier your Aquarium water the more Ammonia/Nitrate amounts will be in your water so don't over do it. Also you don't want to store it more than a few days in a cool place because besides stinking really bad there are chemical reactions (algea growth ect.) that takes place in stored aquarium water that might not be good for your plants.

  • mfn112964_yahoo_com

    My son's science experiment uses aquarium water on sweet peppers. Based the the gathered data, there is a better growth yield on the plants with 100% aquarium water compared to the set of peppers using 50% aquarium water and "pure tap" water. For the peppers with 100% aquarium water, their leaves are larger and grew taller compared to the rest. Also, they have more branches that makes them more roboust. At this time, buds are coming out and more matured flowers are seen 100% aquarium-peppers.

  • joejscott_Gmail_com

    read up on aquponics, animals and plants require almost opposite things to survive, for example we breath in oxygen and expel co2, plants take co2 and produce o2

    also the nitrogens and other by products from fish will be of use to your plants,

    using aquaponics i often see an increase of 20-30% plant size compared to hydroponics and 50-60% over soil alone

    using fish water will only ever benifit your plants.

    Here is a link that might be useful: aquaponics wiki

  • Imani Christopher


    So, I'm not understanding how you are using fish water to water your plants every other watering day if you suggest only storing the fish water for a couple of days... How often do you water? And, do you have any suggestions on how I could store the water for a longer period of time?? I just started my garden, so I am new to all of this. Lol.

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