Nine month update: the fish


Brutus, approximately 1 year old


The fish at approximately 6 months old.

The most notable thing about the fish since you last saw them is that they have grown 10 times their original size. They were in the 10-15g range shortly after I got them, at I’m guessing 3 months old, and they are 90 – 130g now. What seemed like a ridiculously under stocked tank a few months ago, seems well filled now. If you are considering a small aquaponics system with “just a few” goldfish, please have a look at Brutus in the top picture and imagine how he’d enjoy being crammed into a small aquarium (or worse, a bowl, but don’t get me started). My tank is 100 gallons, with roughly 150 gallons of water in the entire system. There are 11 fish in total. Goldfish will grow fairly rapidly until they are about 3 years old, but they do grow throughout their lifespan, which can be up to 20 years. Yes, you can stock an aquaponics system more densely than an ordinary aquarium, but fish still need room to grow and swim.

20140803_152857I’ve changed the diet back from the homemade gel food I blogged about earlier, to a premium pellet for a couple of reasons. The first is that I’ve been sick the last couple of months and I just haven’t had the energy to make the gel, especially since as the fish grew they were eating much more of it. The second is that I’ve found a really good Canadian fish food, Northfin, that contains relatively low-on-the-food-chain ingredients like krill, herring and sardines and no crap fillers. I picked up a small package at the fish store to try it out, and the fish seemed to enjoy it, but at $10 per 100g it was outrageously expensive. I was able to order a 2.5kg bag online for $80, which is still pretty dear, but should last a good while. These are well-fed fish, in both quality and quantity, and I’m sure that that, along with good water quality, explains their impressive growth.


The goldfish gourmet


goldfish gel food

This is what’s for dinner, if you’re a goldfish.

I made up a batch of gel food for the goldfish today. This isn’t exactly a typical goldfish diet, but it’s what some fancy goldfish breeders feed their fish. My fish have more than doubled in size in the last 3 months eating this stuff and they obviously love it. Goldfish often have problems with their swim bladders and end up unable to swim properly. The solution to that is dietary fibre and lots of folks give their goldies peas that they’ve carefully peeled. This recipe includes the peas, and no peeling required. It’s got lots of protein, fibre, vitamins, colour enhancers, and micronutrients. I include a scoop of commercial goldfish pellets just in case I’m missing something. I use gelatin, but you could use agar agar if it’s available. I use sardines and clams for the protein component because, unlike tuna say, they do not accumulate a lot of toxins in their bodies.

Here’s the recipe:

  • 1 can whole baby clams, drained
  • 1 can whole sardines, packed in water, no salt added, drained
  • 1 red pepper
  • 2 small carrots
  • 1 bunch cilantro
  • 1 cup peas
  • 2 cloves garlic
  • 3/4 cup dry lentils
  • 2 cups water
  • 1/4 cup kelp meal (I buy a huge bag from the feed store and feed it to the chickens and garden)
  • 1/2 cup sinking goldfish pellets (optional)
  • 4 packages plain gelatin

1. Put all ingredients except kelp, pellets and gelatin in a pot and bring to a boil. Cover and cook on low for 45 minutes.

2. Remove from heat and add kelp meal and goldfish pellets.

3. Blend with a hand blender until smooth.

4. Bloom the gelatin: Put gelatin in a bowl and add 1 cup boiling water. Whisk until thoroughly blended. Let sit for 5 minutes.

5. Combine gelatin mix with cooked food mixture.

6. Spread on a cookie sheet lined with plastic wrap and let sit for 15 minutes.

7. Cool in refrigerator for several hours or until set.

8. Cut in 1/2″ squares and place in freezer containers. Store in freezer.

Every morning, I take the day’s portion of gel food out of the freezer and put it in a little bowl. It takes only a short time to thaw, at which point I start feeding the gang a cube at a time several times throughout the day. I squish the cube in the water and they all grab a bit, then go chew on it for a while. Whatever’s left gets hoovered up pretty quickly and I never see any on the tank bottom after a minute or so.

This food is pretty high in protein, and so is suitable for younger fish who are still growing. If you have older fish (over 3 years) you could use a smaller amount of seafood, say, just the clams or just the sardines.

This recipe is based on one posted by the folks at East Coast Ranchu.


How I stopped worrying and learned to love the mulm

20140317_110405This lovely photo is a rare look inside my sump tank. The reason I don’t normally show it is because it isn’t pretty. The fish tank drains into the sump by means of a solids lift overflow. This is a fancy name for a pipe that sucks from the bottom. As a result, the sump has got this brown gook on the bottom that looks very much like what you’d think. It’s mulm. Mulm is solid waste material such as plant parts, fish poo and leftover food in various stages of decomposition. Some of it gets pumped into the grow beds, but mostly it just lurks on the bottom of the tank. But wait, I can hear you cry, this is an aquaponics system – aren’t the plants supposed to clean all that up? Well, yes, sort of, but, as with most things biological – it’s complicated. I’ve posted previously about the nitrogen cycle and it’s a huge part of the process of converting fish waste to plant food, but it isn’t the whole story.

Nitrifying bacteria are delicate, slow growing chemoautotrophs which oxidize inorganic chemicals (ammonia and nitrite) to obtain their energy. The vast majority of bacteria species are heterotrophic and use organic compounds like proteins and sugars to fuel themselves. These guys are everywhere, as anyone who has ever found a sandwich from last year in a backpack on the first day of school knows very well (just me?). So the slightly more correct version of the aquaponic story is that fish eat food and excrete ammonia and poo, and heterotrophic bacteria break down the poo into organic and inorganic components such as ammonia, which feeds the nitrifying bacteria. Bacteria also feed on uneaten fish food, dead plant matter, dead algae, dead worms, dead protozoa and other dead bacteria. It’s a bacteria eat bacteria world in there.

Mulm builds up because larger solid particles take longer to break down than small ones. Eventually, it becomes mineralized. Mineralization is the decomposition of organic matter into its component inorganic parts. Some elements, such as copper, iron, manganese and zinc will not be available to plants until mulm is broken down, because they are only excreted in solid waste by fish. Mulm is also a generous source of calcium and phosphorous.

Another result of the decomposition of mulm is humic substances. These are somewhat mysterious molecules that give a yellowish or brownish cast to natural waters and are negatively charged. This negative charge binds with certain micronutrients and keeps them in solution and available to plants. They also prevent some metal toxicity in fish and plants.

Most of the preceding information I gleaned from an amazing book called Ecology of the Planted Aquarium, A Practical Manual and Scientific Treatise for the Home Aquarist by Diana Walstad. I’d recommend you find a copy, or google the author’s name and read her stuff online, because she has a fantastic understanding of aquatic ecosystems. In aquaponics, we are trying to create an ecosystem with terrestrial not aquatic plants, but much of her information is applicable.

Some folks filter out all solids, while others have a much more laid back approach. Systems using deep water culture, or floating raft methods need to filter. Red wiggler worms  help to minimize clogging by solids in media beds. I am of the opinion that letting bacteria do their job to extract all the nutrition from organic matter is beneficial to the plants and the whole system even if it looks a bit messy in the sump tank. No doubt if I was running a commercial system with high fish stocking rates I’d have a different position, but for me, for now, mulm happens.

Week 12 Update

Mesclun mix, cut and come again many times



Rapini seedlings


Romaine, cut and regrown a couple of times already


Swiss chard, not floppy anymore


Munchkin brocolli, though I wish it was smaller

Things are growing in the basement! Almost everything is considerably more robust since the last update not quite 4 weeks ago, including the fish. I am feeding more than twice as much as I used to, yet the nitrate levels in the system are barely above zero, if they are at all. Today Madeleine brought home a couple of Shubunkin goldfish with pretty calico colours to add to the troubling (everyone knows that a troubling is a group of goldfish, right?). Shubunkins are single-tailed hardy goldfish with fancy colours, but not the strange body shapes that most fancies have. Hopefully they will help add nutrients to the system.

We’re eating great salads several times a week and I’m reseeding regularly to keep the greens coming. I add iron to the system every three weeks, as iron deficiency is a common problem in aquaponics systems in general, and particularly in systems with high ph. My ph is still high (8.0 – 8.2), but the carbonate level is gradually coming down due to nitrification. I add 15 litres of water to the system every five days or so, to replace water lost to evaporation and transpiration. Unfortunately, when water leaves the system that way, it leaves its carbonates behind, so I make sure to treat the top up water with acid a day before I add it, which has the effect of consuming all the carbonates. This way the carbonates in the system do not increase over time. Given the good growth of my plants, and the fact that fish and nitrifying bacteria are fine with the higher ph level, I am not making any other effort to reduce the ph, and I am taking it on faith that as the system matures, the ph will drop naturally. Then I will be happy to have such hard tap water to add to the system to replenish carbonates.

I’m still very excited about my aquaponic garden, and I’m looking forward to the even greater productivity that will come in a few months once the ecosystem is fully established.

First greenhouse thoughts

Too much?

Too much?

In my climate, to run an aquaponic greenhouse is to run a heated greenhouse. I can’t do an Eliot Coleman style hoop house with row covers and simply wait out any cold spells. If I am to keep water running through the aquaponics set up, I have to keep the temperature inside at least a couple of degrees above freezing. Even if it’s in the minus crazies outside. I’m a little nervous about that, actually, because if I failed at that, and things froze up, I’d lose more than a few plants. Ice and plumbing just don’t play well together. It’s not just heating though – there are thermal mass and insulation to think about as well.

Another thing to consider is that at very low temperatures, nothing grows very well. Fish metabolism slows to almost nothing, nitrifying bacteria take a vacation, and plants just kind of stay alive, rather than grow. This means that unless I do a lot of heating, and lighting for that matter, I won’t get the same kind of crops from my outdoor aquaponics over the winter as I do in my climate controlled basement setup. So why would I want to move outside anyway?

Moving outside would allow me to expand my aquaponics garden. It would allow me to take advantage of the free sunlight, especially in the spring and summer when growth is most vigorous. It would give me a place to go in the winter to escape the cold and snow. I would hope that whatever heating is required for the winter months would be offset by the reduction in lighting that is necessary 365 days a year in my basement. I think there are calculators online that could help me figure that out.

I’d love to have a large greenhouse where I could set up a huge aquaponics system to grow most of my family’s vegetables for the year. I’d need to have a large heating plant, and quite frankly, if I’m honest, it isn’t necessary. I will still have my main outdoor garden where I can grow lots of storage vegetables and I will mainly grow herbs, greens and salad plants and some extended season tomatoes in the greenhouse. If I keep the greenhouse small, I can keep the heating requirement small as well. I’m leaning towards vertical grow towers to maximize light and space.

Here are some greenhouses that I find inspiring:

Week 8 update

Indoor aquaponic garden

Indoor aquaponic garden

Eight weeks ago, I decided that everything worked and nothing leaked and it was finally time to start growing fish and veggies. I powered up the pump and it has been running ever since. Shortly after, I planted a few plants and a lot of seeds, and shortly after that I installed the goldfish. My system was cycled almost immediately, thanks to a donation of used filter floss from my daughter’s mature aquariums.

As far as the plants go, I’m happy to report that the initial spindly and anemic growth has been replaced by much more robust growth. We’ve been eating salad greens for a few weeks now, and the rapini was wonderful. I never manage to catch rapini at the right time when I grow it outdoors, but this bunch was perfect, and no flea beatle damage! I keep planting seeds to have a continuous harvest.


The “poopies” eat out of my hand.

The goldfish appear to be doing well. They are growing and their colour is nice and bright. Their water is clear, and more importantly, the ammonia and nitrite levels are consistently zero, and the nitrate levels are very low. This means that almost all of the waste is being processed by the system and used by the plants. One of the original fish died, and I replaced him with three more, giving me a total of 10 fish. I’ve been feeding them generously to make sure the plants have enough nitrogen. The fish don’t mind.

I still test my water parameters daily, which may be a bit over the top at this stage, but since the system really runs itself aside from me adding feed, I like to do something. I’ve been recording the water values and anything else I do to the system in a paper notebook, and also in a diary on a site called This is an Australian university research project on aquaponics systems that anyone can participate in. The idea is that many people will add their data and everyone has access to information from other systems. So far there aren’t that many people participating, but the diary displays data in table and graph form, so it’s an interesting way to monitor changes over time.

I’m still very excited about the aquaponics project. I haven’t had any horrible disasters and everything works much the way I anticipated it would. As a proof of concept, I’m declaring this project a success. I’m already thinking about expanding and moving into a greenhouse, but I would miss the constant water sounds from the basement. Maybe I’ll just have to build another system outside, instead of moving this one.

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!