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Thursday, February 14, 2013

No Heaters and the Fish are Still Alive

A picture of one of my bluegills from last summer

One of the most fundamental tenets of medical ethics is primum non nocere, or "first, do no harm." In the practice of medicine, this means it may be better to do nothing rather than commit an act that risks causing more harm than good. When it comes to aquaponics, I've taken this advice to heart when it comes to feeding my fish and heating their environment.

I covered the greenhouse in early January but I didn't get around to connecting my rocket mass heater and solar heaters. Last year I was worried about either exhaust leaks or melting things in the case of the rocket mass heater or pumping cold air into the greenhouse during overcast days in the case of the solar heater. I eventually figured out how to overcome these difficulties. But 24 hours isn't enough time to do everything I want to accomplish in a day. As a result, my lovely heaters haven't been in use this winter. When I say "No Heaters and the Fish are Still Alive," I mean there has been no supplemental heat at all this entire winter.

And yet the fish (goldfish, bluegill) have survived.

I had a scare while we were fixing dinner for Chinese New Year. My son-in-law mentioned the green onions in the dishes were from the garden. Since I hadn't been to the garden that day, I asked about my goldfish. The goldfish live in the sump tank, and the sump tank water levels had gotten low that week.

He said, "I didn't see any goldfish. But the water is only a quarter inch deep in that tank."

I was sure the fish were dead. But when I got a chance to go out and inspect, I saw that the sump tank, though nearly empty, still had a couple of inches in the bottom. The pump is elevated on a pad so it stops pumping water when the level drops that low. The three goldfish were still in there, alive and well though cold.

In the same vein, I've worried about the bluegill. During cold snaps, I've gone for days and even weeks without visiting the greenhouse, much less feeding the fish. Whenever that happens, I begin to worry that I've got a tank full of cold water filled with dead fish. I'm just hard-wired to think an animal has to eat every day. Intellectually I know it's actually more harmful to feed fish when the water is nearly freezing. But the anxiety monster grows until I get a chance to go out and lift the lid of the tank. So far I've not had a single bluegill die.

I did lose my single surviving minnow, a fathead minnow or toughie (tuffie) as they are sometimes called. However, these minnows are only supposed to have a lifespan of 14 months. It's rather astounding that this solitary fish had managed to survive for at least 22 months after I bought him. If I thought my toughie had died of disease, I would have disposed of him outside the garden. Old age, however, isn't a communicable disease.Since the water was near freezing, I slid him into the bluegill tank, where one of the fish made a quick meal of my toughie's mortal remains.

Though nighttime temperatures will continue to drop below freezing, the weather should warm from here on out, on average. More importantly, the days will become increasingly warm, and the longer days will begin pumping heat energy into the greenhouse, to the point that I may have to start lifting the side walls by April or May.

Average highs, lows, and rainfall


  1. Meg,

    I live in Northern Virginia too. I'm thinking about building a green house for aquaponics. I would prefer not to heat it. Blue gill seem like a good choice for this area. What was the water temperature in the Winter? Did the plants grow slowly or die? Finally, is it better to have the tank above ground or below ground.


    1. Hi John,

      I'm sure there were times when my still-liquid water was at 32 degrees, based on the lacy surface ice that formed at the edges. In early February I installed an analog quick-read thermometer in my tank, and it read 38-40 degrees consistently despite crazy-frigid nights. In the past week, the water temperature has climbed to roughly 45 degrees.

      I have utility cables running along the side of my yard that isn't covered with pavers, so my sump is only buried 6 inches deep (leaving 18 inches above ground). My fish tank is entirely above ground. If you can bury your tank, you will benefit from the thermal stability of the ground. However, burying your tank makes some things harder to do (like draining the tank for maintenance or catching fish...).

      Good luck! Would love to have you stop by some time. I'm giving free tours during earth week - you can sign up at