Pond Boss Forums AQUATIC VEGETATION Balance of plants in the environment CATMANDOO Aquaponics Experiment

Early this year we had a Pond Boss gathering at CATMANDOO World Headquarters, complete with the Pond Boss himself, Bob Lusk.

At this gathering, we were introduced to small-scale aquaponics through a friend from West Virginia University. It is a process where fish and plants "grow in harmony together."

In the approximate 8 months since I first learned about this, I've found that it is quite popular with the counter-culture, the drug culture, those who are trying to make food production far more sustainable, and those who just want high-productivity backyard fresh fish and fresh vegetables without chemicals -- in a very limited space, with minimal power requirements, minimal water usage, and minimal environmental impact.

There are multiple great methods for aquaculture. One of the simplest is "barrelponics" where all you need are three plastic barrels. This link provides an entire PDF manual for setting up and maintaining such a system:

Barrelponics Instruction Manual

I was about to setup a barrelponics system,when I was offered two free 300 gallon Intermediate Bulk Containers (IBCs). If you "Google" IBC Aquaponics, you will find more info than you can possibly digest in several days. Interestingly, the IBCs are quite commonly available for free, or at very little cost.

Mine took a little bit (actually a whole lot) of cleaning. But, as of tonight, I've got five bluegill and one small bass living in the bottom portion, and tomorrow I will start lettuce, spinach, beans, and cucumbers in the upper portion.
I'm planning on adding a few 6-8 inch channel catfish tomorrow afternoon. We are hoping to have fresh vegetables for Thanksgiving and Christmas dinner.

I put my system inside a small 6x8 greenhouse that will hopefully stay warm enough until Christmas to provide the vegetables.

Here it is inside my small greenhouse frame, with the tank wrapped in black plastic to keep sunlight from the fish tank, hopefully preventing algae buildup -- and hopefully adding a little solar heating to the water.




The bottom part is home to the fishes, which will get hand fed, based on the water temperature. The top part is filled with about 7-inches of pea-gravel that will become the growing medium for the plants. A simple pump-and-drain system will move water from the fish tank to the grow bed. The growbed will use the nutrients (like ammonia) from the water that has been "fouled" by the fish, and return it as fresh, clean, and aerated water to the fish.



I'll post progress, as it happens.

Very interesting. I will be watching!

Interesting indeed!

Ken, I thought of you as I was cooking dinner last night. Venison steaks, part of a Maitake mushroom (found 3 on Sunday, although one was whacked by frost and soft so I only kept 2) and the last of the greem beans from my sisters garden.

I will be watching this as well, since I hope to try this out next year.

By the way does anyone know what type of Tilapia those are in the manual Ken posted above?

How do you get the solids (poo and other stuff) out of the tank before you spike some parameter that kills your fish?

Just curious.

Winter??? In that unit??? Hmmmmmm....

I am pumping from the bottom of the tank. I don't have my timer on the system yet, but I intend to flood and drain the top every three hours. The biggest issue is getting the ammonia out. But, that is what turns into nitrites/nitrates when I flood and drain -- and that will be taken up by my plants.

As for winter, I will let the system run until we get to a series of days where it does not get above freezing during the day, or the greenhouse gets below freezing and my plants die. My little greenhouse really heats up with just a little bit of sunshine when all the flaps are down. The approximate 250 gallons of water, and the rocks in the top should act as a pretty good moderator of temperature also.

Ken

I have always been under the impression that all living organisms that were specie-specific adapted to a certain amount of sunshine required at least that amount of sunshine to maintain an acceptable level of homeostasis. Your configuration appears to block all sunlight from entering the fish holding container. Will this not eventually cause a negative health effect?

I think it would only cause a negative effect in the summer when the temperature would get extremely hot

The bottom tank actually gets a fair amount of sunlight. Some is direct, but most is indirect. In many of the local commercial fish operations that I am familiar with, the fish are raised indoors, with only fluorescent light, and in general, at far fewer lumens than my water is receiving during daylight hours. From experience, it also seems that fish raised in cage culture prefer to stay under the lids, and not in the open sun.

The photos shown in the post above were taken after dark, but here are a couple from late this afternoon as the sun was about to set. As can be seen, even at dusk, it is still fairly bright.





Yesterday I added five 6-7 inch channel catfish to the five bluegill and the one small bass that I put in a the day before. So far they are not eating. However, the water is only at about 55 degrees F. Tomorrow the greenhouse cover goes over the frame. That should warm the water considerably, as the greenhouse will reach around 100 degrees F, this time of year, during afternoon sun.

This afternoon I planted Alaskan peas, green beans, five kinds of lettuce, spinach, two kinds of cucumbers, and some summer squash. All have harvest days of 50-60 days after sowing. I'm hoping we can have some fresh vegetables for Christmas dinner -- maybe even some for Thanksgiving dinner. Time will tell.

Ken

Early yesterday, a friend helped me put the greenhouse cover on the frame. This was the first time I'd used the greenhouse in the fall. The sun is below the tree line, and the leaves are still on the trees. It will probably be at least two weeks before the greenhouse gets significant sun.

The water tonight was still only at 53 degrees F. One bluegill came to the surface for food.

I built a timer yesterday that allows me to flood and drain the growing area, which also provides aeration to the fish water, eight times per day.

So far, nothing has germinated -- but is has only been two days.

Ken

pretty neat!!

Fascinating stuff, Ken.

Have you thought about the degree of inputs (presumably, electricity for a heater) that it would require to keep the system going throughout the winter?

First things first, of course, but just wondering if you have thought about a six-month operation.

I had wanted to get this thing started back in August, but time just didn't permit that. I'm hoping I can keep it warm enough until Christmas with just the greenhouse. I plan to start it back up again in March.

If it really works, I plan to at least double, and maybe triple the grow bed area. Right now I have about 65 inches of fish in the 250 gallons of water. Most things I've read say that you can maintain an inch of fish per gallon, so I should be able to add a bunch more fish too.

I wouldn't want to try and heat it with anything but solar. I think that would be just too costly. Right now, the only power requirement is for a 25 watt pump that runs for a total of 56 minutes a day (8 times per day for 7 minutes each time).

Ken

Ken you've got an interesting experiment going that I think a lot of people will be interested in, I've been thinking about making a portable structure to cover my little backyard pond in cool weather and grow some veggies in floating islands.

One thing that might help increase light to speed up growing would be putting aluminum foil on walls that don't receive direct sunlight.

Great project.

Ken:

I've been doing some reading on RAS systems. The amount of fish all depends on the amount of filtering area. And, from what I've read, the amount of filtering area is determined more by the amount of food that the fish are fed than by the amount of fish in the system. But, I haven't seen anything written about how the water temp affects the effectiveness of the bacteria in the bio filter. I have a gut feeling that the water temp matters more than people think.

Temperature is critical in many of the processes, both chemical and organic, that take place in an aquatic eco-system. This is especially true of bacteria. Nitrifying bacteria have been reported to function at peak efficiency when temperatures are around 80F. This efficiency drops as temperatures drop until all conversion is ceased at about 34F.
A side note on the amount of food being a main concern. One should also take into account that 85% of the food consumed by fish turns to waste, only 15% is utilized by the fish.
The 1 inch per gallon of water stocking level previously referred to can, I fear, rapidly become problematic unless the filter bed is greatly increased in size and the water turn-over rate is increased proportionately. A turn-over rate of once every 30-60 minutes would seem to be indicated at this dense a stocking level.

Scott and Instar,

I agree with what both of you say. If I go to denser stocking next spring, I'll add more grow beds. When I get time I plan to go to a continuous flood and flush system with bell siphons and a different pump. Right now I'm doing very minimal feeding due to the temperature. I may have to supplement my plant food within the water.

Ken

When I checked my experiment late this afternoon, I found that the lettuce, spinach, and green beans had sprouted.



The water is 62F degrees, top to bottom. The food I've been putting in has been disappearing. Much of it could just be sinking to the bottom, but I know that at least some of it is being eaten by the larger bluegills that I've seen at the top eating it.

The timer I added cost about $16. The pump draws less than 2 amperes at 12 VDC. The pump is on for 56 minutes every 24 hours (8 times per day for 7 minutes each time). That puts me at about 2 ampere-hours per day of consumption. When spring comes, I think I'll make the whole thing solar just to prove to myself that it can be done completely without external energy sources.

Here in my little timer mounted in a weather-resistant housing:


And, here is the little greenhouse with the cover installed:

We had our first fatality today. One of the catfish was floating this morning. I think I'm going to have a second fatality by tomorrow. I didn't have a camera with me when I checked them tonight, but one of the catfish was pretty lethargic, but floating/swimming upright at the surface. It had yesterday's soggy food pellets stuck to it's dorsal fin, and to both of its pectoral fins. A friend was with me when we saw this, and both of us found it quite puzzling. We couldn't catch it to remove the pellets. The bluegill seem to be doing pretty well. They are coming up for food, and they seem quite active.

Since we had the fatality, we thought that maybe the project needed some better water. Some neighbors came over to see if they could assist.



The first hole was so successful, we decided we'd put in another one about 15 feet away. It was a real gusher!




















Actually, these are two 300-foot wells for a new geo-thermal HVAC system we are installing. The good thing is that if we ever need another water well, we know we have immense amounts of water starting at about 40 feet down. They were able to dig two 300 foot wells in less than six hours. But, the 55,000 lb., truck sure made some ruts in the yard after 2-1/2 inches of rain in the last several day.

When is the last time you tested your DO levels?

Not only DO, but I'd get an aquarium test kit and test Ammonia, Nitrites and Nitrates.

Ken,

Your catfish may have died from a spike in nitrites. The symptoms sound like that too. Scaleless fish are very sensitive to nitrites. Fish in the centrarchidae family are not. Yellow perch are quite resistant to nitrites too.

If it was me I would have felt better getting the fish tank cycled first before adding fish. But I can understand your time crunch.

Keep us posted. I am keenly interested in Aquaponics but haven't got my feet wet yet. A local high school that has one of my recirculating systems has it in a greenhouse, and they too want to give aquaponics a go.

Keep up the good work!

Your pea gravel is going to act as a biofilter. I was going to comment on the cycle thing earlier, but let it go. Your solids, without filtering them may become an issue down the road.

I tried some CC once that were given to me. Water parameters all good. I came to probably an incorrect conclusion that they just did not like the confines of that particular tank.

Good luck!

Cecil -- first, I'm really glad to see you back. Before I had the time to actually begin doing the physical work, I spent a lot of time looking at all of the stuff you'd written about your RAS experiments. I even resorted to looking at PeePonics in case it gets too cold to feed the fish!

Instar -- I haven't been able to check the DO in the past several days, as I don't own a meter. But a friend checked it earlier in the week, and we were pretty close to 100% saturation for the temperature. I don't remember the readings -- but he is a fisheries biologist who is into aquaponics in a big way, and he said it looked good.

[I am very fortunate to be able to volunteer at a WVU research facility, where they do aquaponics in a big way, and where I have access to some incredible experts, and equipment. Here is a link to the place: WVU Reymann Farm Aquaponics]

I do have a water test kit, and everything looks real good. My pH is right at 7.0, with virtually no hardness. Here is what my ammonia, nitrate, and nitrite levels look like (left to right) -- virtually nothing showing in the water. The ammonia sample is actually much more yellow that it shows in the photo.



A serious cold front has moved in, and the leaves are still on the trees. My water was at 54.3 degrees this morning, and the greenhouse was 40 degrees. Hopefully, the leaves will start to drop and the greenhouse will warm up.

Those numbers look good to me Ken, I have no idea what happened!

One catfish is missing. The catfish, the bluegill, and the one LMB were all at the surface feeding this afternoon. But, I only saw two catfish. I added five catfish, and two died -- so one must be on the bottom. The small LMB was gobbling pellets.

I'm going to have to grind up some of the the feed. The catfish and the smallest bluegill can't get the AQM 4000 into their mouths very easily.

I switched out the 12 VDC bilge pump for a 330 GPH / 120 VAC magnetic drive pond pump with filter. It should pump about 120-150 gallons per hour at a 3.5-4 foot lift, into the plant area. I'm going to set it to run seven times in 24 hours, for 2 hours each. I'm really short of time in the next two weeks. But, as soon as I can find an hour or so, I'd sure like to get a bell siphon installed so I could run the pump continuously.

The water was still only at 54.7 degrees this afternoon, although it was 70 degrees outside. I added a 16 mil black plastic sheet to the southside of the greenhouse. Until the leaves are off the trees, I need all the heat I can get from what little sun in coming through. I'm hoping this will help. I'm thinking about switching the present fish for a number of small rainbow trout since my water is remaining so cool. I'm just worried that the trout might not have enough oxygen.

Ken

Likewise. Maybe just handling stress for the catfish. They may be more prone to problems in cooler water than the other species.

Agreed. One of my local expert friends also figured it was handling stress. Actually, when I first asked him what he thought might have happened to my catfish -- he said "they died!" So much for expert advice.

Anyway, because the catfish and the small bluegill were having trouble getting the pellets into their mouths, I chopped some pellets. It took a while to find something that would work to make the pellets smaller. My "expert friend" suggested using a small electric coffee grinder. It worked great. The fish, including the 6-inch LMB, really seemed to enjoy the ground pellets. They slurpped down the grounds pretty quickly.

Everything has sprouted. The plants are growing, just a little slower than I'd have hoped.

I'm just getting started in Aquaponics but the text I'm reading says your plants won't thrive until the nitrates get up to a certain level. Makes sense to me.

here's another great aquaponics guide using IBC Totes:
http://www.backyardaquaponics.com/Travis/IBCofAquaponics1.pdf

i've seen systems "balanced" with a reading of 0 for am, nitrites, nitrates.. but my system usually runs at 40 to 60 nitrates

I could not get that link to open.

it's a pretty big file, 37mb,
try here:
http://www.fastonline.org/content/category/4/15/29/

click on the link:
"The IBC of Aquaponics"

I downloaded it several months ago, and it has a lot of good information if you are planning on doing something like I'm doing. As Keith says, it is 37 MB, so it takes a while to download.

Ken

One catfish was floating this morning, and the last one (the one I couldn't find) was floating tonight. It was pretty disgusting. I guess it died a few days ago. I put about 45 catfish from this batch into my main pond, and about 50 in a neighboring pond. I've seen no evidence of them dying in either pond. They just weren't suited to tank life.

The bass and bluegill seem to be doing OK. My ammonia and nitrite/nitrate levels continue low. The plants are growing and green, but I may have to supplement the plant feed, unless I get more fish, and more fish eating more food. The water is still at only about 56 degrees. The 5-day weather forecast shows it getting cooler each day. I expect we'll get our first frost in the next ten days. Lots of deer wandering around, I just wouldn't have any time to butcher one for at least the next week or so.

Unless you can maintain the water temps at a higher level, the fish are probably not going to be eating much as their metabolism is slowing down. The nitrifying bacteria are also working at a considerably lower conversion rate than they would at higher temps so adding a supplement may cause problems if not done very carefully. Temperature is really the key player here.

Unfortunately you are right. As I mentioned above, I had wanted to start about a month earlier, but hours in the day just didn't permit that. I may end up changing the fish out in the next week or two. If I do, I'll put trout in.

If the fish don't work out because of temperature, I may add some worm castings to feed the plants. It is about time to get the worm beds ready for winter, and I'll have a couple of hundred pounds of castings available. I'd sure like to have a fresh salad for Christmas dinner.

In general, this is a learning experience. Hopefully this will give me enough knowledge to make it work reasonably well next spring and summer. I want to expand this as our "kitchen garden" and put in a larger hydroponic system on my pond dam.


Ken

CATMANDOO's Aquaponics Garden is not the Garden of Eden. If Adam and Eve were here, they'd be skinnin' some big furry critters to make clothes so they could keep warm.

I grossly underestimated the amount of sun my little greenhouse would receive in October. I had expected it to be about the same as it receives in late March or April, when the sun is at similar elevations. It regularly reaches over 100 degrees then. I sure was wrong. I didn't account for all the leaves that don't fall off the trees until the strong winds and first snows of late November and early December.

The internal temperature of the little greenhouse stays at about the temperature of the water in my IBC, which is now about the average local air temperature over several days. The water temperature has now dropped to about 49 degrees.

As mentioned above, all five catfish perished. There are still five bluegill and one small bass. They all seem to be quite happy -- they just aren't eating much. However, they did get quite excited this afternoon when I dropped a couple of dozen red worms in, one at a time. Still, they just aren't providing enough food/poop for the plants.

So, as of today, I am trying a backup solution. It was time to start cleaning out the worm farms for winter. I removed a 5-gallon bucket full of worm castings (poop) from one 40 gallon container.

In my small aquaponics growing space, the cucumbers and squash never germinated. In their place, I placed several quart pots. I put about an inch of pea gravel in the bottom of each pot, and then filled the pot to the waterline with worm castings. I sowed a variety of lettuce, some spinach, and a few "French breakfast" radishes into the pots. I then added about another half-inch of worm castings over the seeds.

I also reset the water pump timer so that it only runs for 10 minutes every three hours. It takes about six minutes to flood the growing area to just below the top layer of pea gravel. This will hopefully move some nutrients from the worm casting pots to the other vegetable roots.

The peas seem to be doing OK. The lettuce and spinach have good color, and look good. They aren't growing as fast as I had hoped for.

Besides giving up on the cucumbers and squash, I also gave up on the green beans. The beans germinated, but they were really far behind everything else. I believe it was just too cold.

Here is what the grow bed looks like with the addition of the pots with worm castings, that have been sown with various kinds of lettuce, spinach, and radish.

Interestingly, the "lost catfish" showed up this evening. I've been feeding lightly about every third day. Tonight, the little catfish showed up skimming the floating food.

The peas have grown about 2 more inches in the last few days from the pictures above. The other plants are growing, but not very fast.

The water is at 50 degrees F, and that was the temperature of the greenhouse near sundown this evening.

We had a lot of wind and some heavy rain today. Lots of leaves came off. That could be good for heating the greenhouse. But, the forecast is for temps in the 20s over the weekend, with the potential for a major coastal storm, and if not, they expect we'll get some snow!

Well, sounds like you're holding steady on water temps, but the plant growth is pretty cool, so something must be working okay. Keep us posted on the weekend weather!

Its cooled off here too at least in the mornings. The days are still pretty nice.

i just got 4 IBC's this week (two 330's and two 275's)
i set up an 8'kiddie pool in my basement, and seeing it sitting there, i had to do something with it so made a filter out of a 55 gallon barrel (now i can make real growbeds for the pool!) and threw in 50 rosy red minnows and a couple dozen crayfish..after i get growbeds built, i'll be putting the yp and bg in the pool
(i already have about 45 fish - yp and bg - in my aquaponic system in the basement, using three 55 gallon glass tanks, growing green's using flourescent lights..
this aquaponics stuff is addicting!

Keith -- fantastic.

How about some pictures, or even a new thread on what you are doing? As I've gotten involved with this whole thing over the last year, or so, I'm finding that it is becoming a pretty serious hobby and commercial movement amongst many.

I'm not sure what will happen to my experiment over the next 36 hours. We are expecting 4-8 inches of snow, and temps in the upper 20s. I don't know if the inside of my little greenhouse can withstand such outside temps without killing the plants. I'm not sure if my little greenhouse can even withstand that much snow.

It was 53 degrees outside when I went to bed last night. It was 41 degrees in the little greenhouse this morning when it was just 30 degrees outside. I think we are somewhere in the high 30s right now, and is becoming increasingly overcast.

You have a certain amount of built-in insurance from the cold provided by Ma Nature. As water reaches 32F, it releases latent heat. If your greenhouse is sealed adequately, this should protect your plants for short (several hours) periods. You might consider adding a small heater before the winter temps become too harsh, however.

i'll be taking plenty of pic's along the way, and will start a thread soon

Unfortunately, when it gets cold here, it gets cold and stays cold. Generally, we do not get above freezing from around Christmas until sometime in February. Some years that extends well into March. Sometimes it starts by Thanksgiving. We are just above freezing right now, with sleet coming out of the sky, and expecting 5-8 inches of snow by tomorrow afternoon.

Unfortunately, a small heater won't do. A big heater would be needed, and that is just out of the realm of possibilities. I'm guessing that a wood stove would take several of cord of wood to keep the water at 50 degrees during our cold season.

The more info we have, the better for everyone.

I've renewed my IBC-tank aquaponics experiment and project. This year's main garden is 50' x 100'. We also have a "kitchen garden" of several 4' x 4' x 14” raised beds/worm farms, plus other containers.

We moved the aquaponics system to my younger son's place, as my DIL would really like fresh tomatoes, cucumbers and salad greens out the back door. But, their schedules don't really support a conventional garden.

Today, we used my semi-trash pump to fill the tank with creek water to the 275 gallon mark. A shovelful of fresh chicken droppings was added as a "starter". Over the next couple of days I plan to add a couple of tomato plants, some lettuce and 5-10 mature fatheads. I'll keep putting fatheads in until they stop dying -- if they do. In the meantime we'll be keeping a watch on ammonia, nitrites, nitrates, and pH,to adjust as necessary. When things stabilize I plan to start adding HBG. Then I'll add more tomatoes and a couple of different kinds of cucumbers. It has room for at least 12 "major" plants like tomatoes and cucumbers, and room for pretty regular harvests of salad greens.

I'll start adding progress photos in the next few days.

I know you didnt ask me, but i'll give my 2c on PH:
I consider 7-7.2 optimal. [Most] Plants prefer PH a little lower and [most]fish pref it a little higher. That's the middle ground. If your PH is low you may want to do something to bring it up, However, i dont adjust PH down because it is going to go down slowly over time due to the nitrification process.

With that said, after years of tinkering with ph i just started to use expanded shale for my grow beds. It's cheap, relatively light and porous (which provides great surface area for bacteria.) People say expanded shale is ph nuetral but none that i have bought has ever been ph nuetral. It usually buffers my system at ph 7.8. It's a little high for plants but i havent had any serious problems with nutrient locking. And my ph is pretty much bullet proof from swings. I havent checked it in months because it doesnt move.

If you use river rock, it will probably have some limestone in it and buffer your PH as well. Some people consider that undesirable. i consider it low maintenance.


If people are interested i can start a thread showing some of my aquaponics systems.

brian

I haven't checked the water yet, but since it came from a stream after a week with lots of rain, I suspect it was pretty close to 7.0. My ponds stay locked at about 7.0. I also expect that if it isn't neutral now it will settle out at about 7.0. As Brian said above, that seems to work for both the plants and the fish.


It is 36 degrees outside this morning, and it is supposed stay cold for the next few days. I suspect it will take a bit to get the water to do much of anything until it warms. I'm just going to run the pump continuously until the water warms, before I try to do anything more with fish or plants.

.

I think that would be very good. Cecil's RAS thread has been very valuable. And, I think that those of us on this site look at aquaponics somewhat differently from people on the aquaponics sites. The things done in the past for raising fish in tanks by Cecil, Condello, Theo, etc., have been helpful to many.

Here's another vote for showing your system Brian.

another vote to get your thread up brian..
i'll have to update mine as well. i just topped off all 4 growbeds, the gravel had settled and the top layer was getting a little to wet..
got some asparagus, onions garlic and chives in, but i still have to finish planting the rest of the growbeds
i was working most weekends from last fall through spring, and my plants got a little out of control.. i only lost a few tilapia over the winter and 2 eggbound yp.. but 5 baby tilapia made it through the winter and are growing fast in their own tank..
found 4 berried crayfish last weekend too.. i've had 6 hatches of marmokrebs, the bg and yp love them.. i think i've put 40 or so larger crays in the ft to grow out and keep making babies.. still trying to figure out kind of structure i can put in - right now i'm using a bunch of pvc cutoffs with one end capped

Hey Brian,
We would all love to see your system, so post away! Should be really cool!

We also need to resolve this salt issue with Aquaponics. Any technical insight would be welcomed.

Don't be shy with any other technical details as well. Get right into it!

Thanks!!

And another vote!

Me too.

Two days ago I added six 3-inch tilapia and six more 5-7 inch bluegill to the tank. One of the tilapia and one of the bluegill died yesterday. It was an hour trip from my place to my son's, where the tank is now located. I think they may have died from stress or temperature shock.

The tomatoes, peppers, and lettuce are producing. The color of the tomato, pepper, cucumber, and squash leaves are all dark green, and the fruit is great. The cucumbers and squash don't yet have blossoms. My son said the lettuce was delicious and the jalapenos in the accompanying salad required a couple of glasses of milk.

When I did a water test this afternoon, the ammonia, nitrites, and nitrates were unmeasurable. The pH was at 7.1.

I'd appreciate any guidance. I'm thinking of adding about 30-40 more inches of bluegill tomorrow because the nitrates are so low.

Any thoughts?

Don't add more fish load than your filtration and Flow Rate can handle.

If my ammonia, nitrites, and nitrates are immeasurable -- why not add more fish?

From my measurements, it seems that I either have too many plants, or I don't have enough fish.

I've got a zillion BG I can sacrifice, and it appears my tilipia are reproducing, so I probably will have a few extra there too.

I still have room for more plantings. I would think that I could safely add more fish, in increments, while monitoring the ammonia, nitrites, and nitrates. D.O. remains high. pH remains neutral.

Am I doing something wrong that I just don't see?

If you can add more plantings, then you will be adding filtration (bio-conversion). Adequate flow rate is paramount in order to maintain Oxygen levels.
I can't see where you are doing anything wrong, just a friendly word of caution.

You hope ammonia and nitrites are all ways zero. And zero nitrates is not necessarily bad. Unless you have added additional grow beds, your IBC top grow bed only has about 45 gallons of substrate. I think your max fish load should be about 7 lbs at harvest time.

Incremental adding fish is a good idea.

brian

catmandoo, how are your plants being pollinated(sp)? If they're outside, I understand.