Aquaponics Garden Part 13 – Weighing the options

A chubby goldfish

A chubby goldfish

After getting the aquaponics system all set up in the basement, I had no appetite for spending any more money on this project. One thing I did buy, and I’m very glad I did, is a digital scale. If you are doing aquaponics or thinking of it, I recommend you do, too. My scale was only 15 bucks, but it does everything I need: it holds up to five kilograms, it has one gram accuracy, and it has a tare function, meaning you can zero the weight of the container.

The thing that prompted me to buy the scale, was the issue of how much to feed my fish. I don’t have very many fish, and I want to maximize their ammonia outputs without over feeding them. Young fish can be fed 2 – 3% of their body weight per day, but I had no idea how much that was. So I weighed my fish. It turns out that my fish were about 12 grams each, times 8 equals 96 grams of fish. So I can feed them 2 – 3 grams of dry food per day. My next problem was that I feed a frozen gel food in addition to pellets, and I needed to find out what percentage of the gel, by weight, is food and what is water. I weighed out some gel food and microwaved it until it was hard, then weighed it again. It turns out to be about 20% dry food, so now I can figure out how much to feed. I usually feed about 8 grams of gel and 1 gram of pellets per day, about 2.5 grams of dry food equivalent.
20140113_202234In another post, I mentioned that I add iron to the water to prevent iron deficiency in the plants. The recommended rate is 2 mg of pure iron per litre of system water, every 3 weeks, which in my system comes to 14 grams of 7% chelated iron. I don’t know about you, but I’m not very good at eyeballing powdered iron, and the scale takes all the guesswork out of it.

Today's rapini harvest

Today’s rapini harvest

I’ve also been weighing my harvests. I keep a system journal with all the water parameters and everything I do or add to the system. Knowing how much is coming out of the system is just as important as knowing how much went in.

So if you are making a list of required equipment for your aquaponic project, don’t forget the digital scale!

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