Aquaponic Gardening

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I am new to aquaponics and really interested in starting my own system. I have taken Sylvia's and Alan's course on it and, having just finished, am ready to get it going. 

I do, however, have a few questions and would greatly appreciate anyone's input on these:

1. I live on the 14th floor of a decent-sized apartment and am thinking of a 40 gallon fish tank for a 6 cubic feet grow bed with a sump tank. The weight totals about 928 lbs. and would span over about 43 sq. ft. Does this sound reasonable or would it be too heavy?

2. I was wondering how exactly I would calculate the volume (and weight) of my grow bed. 6 cubic feet (1x2x3), according to the course, would require 300 lbs. of grow medium (using LECA). The course also said that 40% of that grow bed volume would be water and 60% grow medium. I am unsure of how exactly to calculate the volume of grow media then. Do I figure enough grow media to first fill the bed without water or do I take the volume of the container and fill the grow bed with 60% of grow medium and then let the water fill in the rest of the 40%?

3. How necessary is a sump tank for a system of this size? If so, would an 18 gallon sump tank be a reasonable size for this system. 

Thank you so much. I greatly appreciate it.


Adam Richards

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Hi Adam, Sorry you had to wait so long for a (visible) reply, but here you go:

1. System weight:

  • Try a thought experiment: How many average (200-lb) guys standing on your apartment floor inside the footprint of your system is the weight equivalent to? Will five guys staying there 24x7 inside 43 sq ft cause a problem?
  • As you were thinking (based on the information you shared) it is not the weight but weight distribution that determines the effect of your system on the apartment floor. Right now, your system occupies a space less than than 7 ft square. You could move a third of the system weight further—your 330-lb aquarium—to another location and pipe the water further to be safe. Might look nicer, too.
  • LECA was a great choice for an apartment, and as long as yours is not too old (or had previous flooding that weakened the floor boards) you're probably fine.
  • System leaks are your true enemy. Speaking from too much experience, water in aquaria and growing bed is one accidental siphon or one plumbing glitch away from disaster. If you don't own a wet vac, BUY ONE. When filling systems, I also use a water flow timer so that it turns itself off even if I forget. 

2. Calculating volume and weight of the grow bed.

  • Your LECA volume is the same as your grow-bed volume minus freeboard. Forget about the LECA weight, since that varies with brand and moisture level. For your 12-inch deep bed, two inches of freeboard should be fine, making it 10/12 * 2 * 3 = 5 cu ft or 37.4 gallons. 
  • Although you have 60% growth medium, it is 100% of the media bed volume since the water will fill the spaces between and inside the LECA, up to about 1 inch below the top of the dry LECA layer you need to prevent algae growth.
  • In my system, I fill the the 12-inch bed with 11 inches of gravel or LECA, then fill the water to about 10 inches using the height of my bell siphon.
  • Calculating water in your bed: If you filled your 1 x 2 x 3 bed up to 10 inches of water (37.4 gallons) and media displaced 60% of that, you would pump 37.4 gal * 0.6 = 22.5 gallons (give or take, since the porosity of the LECA is an unknown factor.

3. Do you need a sump? YES!

  • The fish would panic every hour, as more than half their aquarium water drained out (fish are hardwired to be sensitive to half their water disappearing).
  • At a minimum, you'll need enough of a reservoir to hold the 22.5 gallons of grow bed water plus the water needed left in the bottom so your pump does not lose prime.
  • Best is to have a reservoir that holds ALL the aquarium water plus the water for pump prime if you ever need to take the tank off-line. 
  • If you already got the 18-gallon sump, keep that in reserve for an isolation tank for new fish or if you need to treat fish with anything that might impact the rest of the system.

I hope this information was not too late to be helpful; or failing that, was at least interesting. --Dean

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