Something’s fishy….

Okay…so how many of you keep freshwater fish in an aquarium?

And how many of you who are fish owners also use the waste water from the tank to give your plants a nitrogen pick-me-up?

We’ve kept freshwater fish for nearly twenty years.  At the moment we have two aquariums, full of various species of tetras and two very whacky golden Chinese algae eaters (Gynocheilus aymonieri).

We don’t keep live plants in our tanks, although this is something I would dearly love to get into – our algae eaters are very fond of digging, however, and they do enough damage to the plastic plants and ornaments we have.  One day, perhaps, when we get some more laid-back fish, I’ll give the live plants thing a go.

Our aquariums have been in place a very long time now, so we have a pretty balanced system, plus we’re very conscientious about the amount of food and the types of food we give our fish so that we’re not generating excessive waste material in the water.  Too much waste from decaying food and poop = a proliferation of nitrates, which are toxic in large amounts.  To keep our fish happy and our system running smoothly, we do a 1/3 water change and clean the filters once a month, and we change out the filter media two or three times a year.  Because we’ve closely regulated the numbers of fish we keep, this schedule seems to work nicely for us.

Whenever we do a water change, we save back some of the water and I give it to my houseplants.   I don’t add any more fresh water – I just pour it straight out of the bucket into a watering can and then into the pots.  The waste water makes an excellent fertilizer, and because I only apply it once a month, I don’t worry about over-feeding.  In the summer, I also take the bucket outside and dump the contents over my flowerbeds.  Why throw this free fertilizer down the toilet?


An aquaponic system is a working cycle that highlights fish/plant interaction.  Check out this aquaponic set-up from Milwaukee for a brilliant example of what can be done with some space and expert know-how.  Note the use of watercress as a water filtration aid.

Finally, read about the chemistry of nitrogen cycles from a plant perspective here.  And then check it out from the fishy side of things here.

Related posts:  Chez worms.

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