Sustainable, Renewable Fertilizer

I love to garden, and to do it organically.  I don’t see the point of growing my own food if I’m just going to dump the same chemicals on it that they do with the store-bought food. Why put in all the extra work?

I began to run into a problem with fertilizers, or rather lack of fertilizers. They do sell organic fertilizers–like bone and blood meal –in the stores, but they are very expensive, and–being a vegetarian–the thought of adding ground up animal parts to my garden was less than appetizing.  I don’t want my veggies to be higher up on the food chain than I am.  Compost is good, but my seedlings needed some more food, as well as my tomatoes and other heavy-producers during peak season.  I did some research and ran across aquaponics, which is the simultaneous raising of food and fish.  The water from the fish tanks (which is full of nutrient rich fish poop) is cycled through raised grow beds.  The plants absorb some of the water and all of the nutrients and return the now clean water back to the fish tanks. A very elegant system.

I didn’t have that much start up-cash or space available, but didn’t see why I couldn’t use a modified version of aquaponics. I had an old 35-gallon tank and stand gathering dust on the porch (even had the gravel and decorations!), so I bought a $10 air pump and stone, a big $10 box of aquarium salt (not table salt-it has iodine in it), filled the tank up with water and the appropriate amount of salt and let it sit for a week to leach out all the chlorine.  It may seem strange to add salt to a fresh water tank, but it is absolutely necessary for a healthy system—fish need electrolytes too!  Every natural freshwater system has salt, we humans just filter it out before we use it.

After I was sure it was safe for fish, I added $2.50 worth of feeder goldfish ($0.13-$0.15 each) from the local pet store.  I didn’t add anything else except goldfish food.  I chose goldfish because they were cheap, hardy, would survive our mild winters outside and produced a lot of waste.


The tank took some time to get established. Several of the fish didn’t make it, which I was expecting (it takes time to get the right balance of good bacteria going in a tank.  Do yourself a favor and don’t name the fish).  I did not use any filter but did keep the filter assembly going to provide additional aeration—there just wasn’t a filter in it.  After the pump died I replaced it with a second bubbler. Any fish that died got buried in the garden as fertilizer.  Once a week I used a small aquarium gravel vacuum to siphon out 5 gallons of water from the tank, all from the bottom where the waste had settled (to keep it hygienic in there).  After about four weeks I decided that the tank was ready—my fish were very active, no longer acting stressed and there were no unpleasant smells coming from the tank, all of which indicated a balanced system.  With this type of setup, once established there should be no “fishy” smell or anything unpleasant coming from the tank—you shouldn’t be able to smell anything at all, even while leaning over it.  I have never used a ph or nitrogen test.  My nose and my fish tell me what’s going on.    

I very slowly started to increase the amount of water I removed from the tank every week, fist ten gallons at a time, then fifteen.  Each time I refilled the tank with the garden hose and added more salt.  I carefully watched my fish after the water change, and if they acted stressed for more than a few hours I cut back the amount of water I removed the next week.  If, a full day after the water change they still seemed to be struggling, I added more salt to help them out.  Goldfish love salt.  All that water I’d been harvesting out of the tank went into the garden, and my tomatoes and zucchini were loving life.  I even began to notice a small growth spurt from my plants a day or two after watering with the tank water.

It took a good 2-3 months total to get the tank fully established and at full production, and I have had my tank going for well over a year now.  I harvest 20 gallons a week from my 35-gallon tank, enough to water two 8X4’ raised beds once a week. I ended up with 14 goldfish, which are now getting rather large.  I will soon have to start harvesting twice a week—I’m thinking 20 gallons on the weekends and 10 gallons in the middle of the week. The tank stays on my screened porch, so messy water changes are not an issue.  My fish only act stressed for an hour or two after their weekly water changes now, and did fine over the winter.  I still had to do the water changes, and just dumped the water in the raised beds.  Nutrients would still be there in the spring.  If I ever decide to buy another tank, I’ll just use one week’s harvest to immediately establish the new tank and save myself a few months.  

Fist Tank

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