Backyard Aquaponics
A place to discuss aquaponics

This is my most recent little aquaponics project, coming from a hobbyist aquarium background...

We have a 75 gal freshwater aquarium in our office, as something to distract us from work occasionally. I let the staff help decide what fish to stock it with and they fell in love with Silver Dollars (Metynnis argenteus), among other things - Pristella tetras, Otocinclus and Metae Corydoras cats, a pair of nice Clown Panaques (Panaqolus maccus).

Problem is that the Metynnis are vegetarians and eat ANY plant material in their tank... It cycled nicely with gradual introduction of animals, some gravel out of our established turtle tank to seed it, and a few plants with which I could keep ahead of the Dollars when they were little. We have a ton of filtration including under gravel panels (I'm old school) with a combination of powerheads and bubble risers, plus a good sized canister pulling up through one panel. With NO plants left and plant/wood eating fish (the Panaques actually eat waterlogged wood) pooping up a storm, nitrates have been a constant battle. I've stayed reasonably well ahead with water changes but have been trying to engineer a solution.

I started looking at refugium/sump answers but the combination of limited space, the requirement that any system be "workplace appropriate" (i.e., not a bodged-together pile of crap), and a high price to pay for flooding argued against that...

...SO I built a little aquaponics unit to perch on top of the tank over the weekend.



Because all I cared about was trapping nitrates, I went with decorative houseplant stock (Epipremnum aureum or Pothos) that (a) does OK without serious lighting, and (b) thrives with wet roots. This allowed me - theoretically - to get by with a constant-flow system rather than an ebb-and-flow answer with more moving parts - bell siphon, timer, whatever.

Total cost including the plants was about US$35, including a window box planter, crushed lava stone for planting medium, a piece of 1/2" vinyl tubing, and plants (all from Lowes home store), plus a neat fitting kit from the local hydroponics and home brewing outlet.



Water is pumped into the system from an existing powerhead (first photo below), up to one end of the box, across the box and through the medium, then out the overflow (second shot, below). The overflow is a 3/4 bulkhead fitting, while the inlet is 1/2 inch. I think we're probably moving about 200gph through the box.





The Pothos is planted with bare roots in the crushed rock, so it's easy to add/remove/clean the box. I tried to keep it away from the inlet/outlet fittings but it's easy to keep an eye on. The box drains straight down into the tank, providing a nice source of aeration.

It's been up for 48 hours and I'm taking daily water readings. No measurable change yet, of course, but I'm hopeful. I'll update here as we learn more but so far, it meets all of the design criteria.

Kirk in Syracuse, NY

Just short of 10 days running and there's been no measurable decrease in nitrate levels (upwards of 40ppm with a typical aquarium hobby test kit). I know I was optimistic but the plants are showing growth and I thought that with that volume of greenery I'd see some kind of change before too long.

I wonder about the influence of water chemistry on nitrate uptake. Anyone know anything about the influence of pH (we're at about 6.8 ) and/or dissolved chemicals on on the process? Again, it's a full flow system with semi-aquatic plants.

Thanks for any ideas,

Kirk

EDIT - here's the missing image from my first post. Sorry about that.

the planter looks like it could have more media in it, usually the surface of the media is dry with the water 50mm below?

That is brilliant! I think every office and every aquarium should have one. Except for marine tanks although I'm sure there would be some plant tgat would tolerate the salt. If there is and someone knows please reply.

The growth will have used nitrates. The reason you can't measure the decrease might be due to many things. Things I can think of

Not enough to make it measureable
Removal of some nitrates have made it possible for conversion of more nitrite to nitrate
The build up of nitrates you would normally get in the 10 days may have been removed by the plants rather than by water changing that might have occurred otherwise
Could the water be a little concentrated because of evaporation as it is now circulating in the open

I would give it a little longer.

I went back and forth about how much medium to put in there. The drain hardware (like this)...



...has incremental settings (spacers tubes) for water depth, so I had options of where it is, too shallow, or too deep. I opted to put in less medium rather than more, figuring I could add more easily than subtract once it was up. I kind of figured medium level relative to water depth was less important with a constant-flood deal. Maybe I'm wrong on that. How do the two variables influence chemistry? I'll watch that, regardless.

I did throw a 30 gallon water change at it at the day after I posted, thinking kind of like Colours mentioned - that maybe it was just keeping up with NEW nitrates. I'll do that a couple more times and continue to monitor. I also figured the other day that the more growth we have, the more food the plants will need. I picked the pothos because it grows like a weed.

...and I WAS a little surprised at how much the water level dropped in a week. It might be "observation bias" because I'm paying more attention but it does make sense that the greenery is transpiring water out of the system. Another good thought.

Will continue monitoring. Thanks for the ideas.

K

Update, a little more than 3 weeks into the experiment...

We've got a pretty good crop of new leaves on the Pothos, and I do believe that we're making headway against the nitrate buildup. The level isn't going down but it's not going up, hanging tough at 40ppm with just one 20 gallon (25%) today since the last one noted above.

To double check my reading (I'm actually a little red colorblind which some would argue makes me an unreliable color card checker), I retested with 50/50 tank water and RO out of the water cooler (zero nitrates). Being lower on the scale made it really easy to tell - with an indicated 20ppm - that we were still at 40. I think we're making headway.

Complicating the math perhaps, I have lost a few fish in the past week - Otocinclus suckers - to some kind of wasting ailment. This means there's less load on the tank which would contribute to improved nitrate numbers.

Kirk

PS - Noticed something I missed above. Ammonia and nitrite levels are immeasurably low, so the tank is fully cycled and working effectively in that regard.

Indoor ornamentals aren't great at taking up nutrient. Hopefully it will keep up with your nutrient load.

If they're putting on biomass, the plants must be getting the nutrients from somewhere?

That's my thinking, obviously. More as it happens! I figure they can't be making the nitrate level WORSE, right?

K

UPDATE

As the pic above shows, Sr. Pothos is doing pretty well. We've added some new growth but honestly, I expected more vigorous increase in size, based on past experience with this weed. I've also had to pick about a half dozen leaves that have been yellow or stunted - likely from having its feet too wet...?

Good news is that I'm pretty confident that my little aquaponics system is taking some of the nitrates out of the fishes' water. I'm changing the same amount of water, at about the same frequency, and the level is steadily - if slowly - decreasing with each change. Simply put, I'm ahead of the levels with my current regimen rather than losing ground. I wonder though if there's room for improvement.

Remember that at this point we're using a dead-simple, constant flow system. Does anyone know if an ebb-and-flow system - with the roots drying out periodically - is likely to change growth and/or nitrate uptake, all other things being equal? I'm inclined to think "yes" but it's already been suggested here that tropical/subtropical houseplants maybe don't need all that much fertilizer, and remember that i don't have any extraordinary lighting contributing to photosynthesis.

Thoughts?

Kirk

Update update...

As an experiment, I took out one of the spacers in the drain back tube, so lowered the water level in the tray about 3cm. Interestingly, water is wicking up through the cheap-o lava rock media I used so it remains damp all the way to the top. I'm still using a constant flow pump. I'll be watching to see if there's any change in growth or vitality of the plants with their roots less submerged.

K

So, the lower water level resulted in droopy plants. I've raised the level back to where we started.

I'm also working on a new addition - a sump with aquatic plants, artificial light, and a circulating pump. Sort of a decorative pond in an $11 planter mounted below the tank.

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