Backyard Aquaponics
A place to discuss aquaponics

First off I have to say that this is a great site for information, particularly about GB based aquaponics. The majority of questions I came here looking for answers I have found.

I'm not really ready for my formal system introduction as so many of you look for in these posts because I'm still working it all out. Like another poster I saw, I'm in an information overload situation right now. Generally speaking I'll have a 700+gallon FT (2600+ L), and ultimately 2 4ftx16ft raft type (DWC) growbeds (128 square feet or 11.9 square meters). I'm planning on a fairly dense stocking of fish, with sequential harvests during the season when the fish hit particular size goals, thus keeping my bioload at the upward end of it's potential through as much of the crop as possible. Also, this will be 100% indoors.

At this point I do have a few questions, with many more to follow I'm sure.

1. Solids removal. Very important to say the least. With GBs, you all tend to want the solids to make it to your hydroponic component. In my DWC I do not. Therefore I need a good solution for some thorough solids removal. I had thought about having a sumpless system, and have the pump draw from a suspended drain near the bottom to facilitate solids removal from the FT, then forceably passing that through a "sock" type filter(or multiples if needed as I am unschooled in the flow rate of water through these micron sized socks). The filtered water would collect in a sump of sorts and then simply gravity feed into my DW beds, and gravity feed back to the FT. Definitely a condensed explaination.
Another solution was to build a separate filter using a 30 or 55 gallon plastic barrel and basically create a large aquarium filter, with multiple laters of filter pads and bio balls, using a pump in the tank to feed this filter and it gravity drain back into the FT.

Opinions?


My other question was this... after having read many many threads on members systems, I have yet to come across good information about fish and other animal harvests that your systems are putting out. All I can get out of those threads is that the fish are there primarily to create waste, with only an occasional fish making it to the dinner plate. Can some of you system posters lay out just how many fish/red claw/etc. you harvest per unit of time?

Thanks for your time,

David

Welcome David

Many people dont post every harvest of fish, they just harvest bit by bit... I had a great harvest on my first crop of Barramundi - 19 out of about 23 or 24 made it to the table
My second lot (silver perch) got sucked up by my pump and became plant food that way (sttep learning curve) and my third crop of Barramundi died due to power failure in the middle of the warm season(all 90 odd of them ). And then I lost a heap or redclaw and Jade perch to white tailed rats!!! But a handfull survived and I will harvest some as soon as the new (very small) Barramundi are big enough to replace their nutrient that the removed Jades would have... Gone Fishin has for example slowly harvested from his tank over quite a few weeks...

Hi David... and welcome to the forum... sounds like you're aiming for quite a large intensive system...

But, sorry... I think you need to put your plans on hold... until you've researched the UVI raft model, general RAS aquaculture... and aquaponics... a lot more thoroughly...

Stocking density is totally related to filtration capacity... regardless of whatever "model" you employ...

Traditionally, in flood & drain growbed aquaponics we suggest a stocking density of 3kg of fish per 100L.... with a filtration capacity that at a minimum equals your tank capacity..

In your case 700gal (2600L).... which would allow for about 80-100 fish... MAX.... with at least 700gal of filtration capacity...

While Tilapia can be stocked at much higher densities than other fish species, they're still dependant on fitration capacity, water volume turnover and aeration...

Setting up a ...



Just isn't going to cut it... even in a straight RAS, or UVI style system... for anywhere near even a 3kg/100L density...

And would require constant, probably daily, maintenance when youre feeding heavily...

To supply 4 rafts of that size.. you'll probably want to stock at least 3-400 fish... way beyond the capacity of your tank ... IMO...

And would require probably at least a 500gal solids filter/digester... swirl filter etc...for even half that number...

You'd also have to heavily oxygenate your fish tank, solids digester... and/or your raft beds...

Hi there and welcome.

Yes definitely read up on the UVI style aquaponics. Friendlies Aquaponics in HI does raft systems. Morning Star fishermen here in FL also does raft systems.

I will disagree as to the numbers of fish in a 700 gallon tank. I have over 100 fish in my 700 gallon fish tank. However, I have some where on the order of 1400 gallons of flood and drain gravel beds supporting those fish. I believe I could probably support over well over 200 one pound fish in my system but I haven't pushed that. I am providing plenty of air to the tank and it is getting continual flow through it.

Some people focus more on the veggies and other people focus more on the fish. I think my system has been supporting the fish better than the veggies so far (my system pH is kinda high so veggie production isn't as good as it might otherwise be.) We could easily be eating fish every week. I have channel catfish and tilapia currently. Since the channel catfish continue eating and growing even at somewhat cooler temperatures, I rate the catfish and tilapia growth as being pretty comparable in my system with my weather conditions.

Ah.. but the essential point TCL... is that you have filtration capcity in the order of 1400 gallons of flood and drain gravel beds supporting those fish.

The figures I suggested were a max for a minimum of filtration capacity equal to tank capacity ....

A 1:1 ratio ... that these days seems to have become a norm... .... rather than the original suggested 2:1 ratio... that you have employed...

And that is the whole point that is so constantly overlooked... particularly by those wishing to raise their stocking densities.....

It is ALL about filtration capacity.... sized to the maximum demand in your system when your fish stock is at harvest size and maximum daily feed rates....

And the supply of sufficient oxygenation for that level of demand...

Definitely, doing a raft system, it will need swirl filters, settling tanks, degassing, lots of extra aeration and enough bio-filtration to support the fish/feed load.

Actually I have studied the UVI system, information from Mike Sipe about tilapia in particular, and lots of information from the SRAC here in the US that directly relates to stocking density, filtration area, etc. Much of the information I have states that stocking densities CAN be as high as 0.5lbs/gal. That's...what... 227g per 3.785 liters...or 60g/liter? So yes, that's about twice what you state Rupert, but I got that stocking density from more than one published source. As for filtration capacity, that's related on your rate of feeding... how much food you're putting into your system, and is indirectly related to the amount/size of your fish stock... true? I took published numbers from both the UVI material and other sources and came up with the absolute maximum for stocking, and the values for how much raft growbed would be needed. Never once said I was going to push it that far.

The numerous sources I have read have said the following:

For a 75 cubic foot tank (8ft diameter round, 2ft deep)... that's about 560 gallons.
At 0.5lbs/gallon that's a critical bioload of 280lbs of fish. The SRAC states, "In general, the critical standing crop in aquaponic systems should not exceed 0.50lb/gallon. This density will promote fast growth and efficient feed conversion and reduce crowding stress that may lead to disease outbreaks."

The raft growing area available for the nutrient load to carry this max fish load is based on feeding.

At a rate of feed of 1.75% of body mass per day that would be 4.9lbs per day (2224.6g)
The waste treatment capability is 180g feed/square meter/day
That comes to 12.36 square meters, or roughly 4.1 4x8foot plots of raft style hydroponics(2 4x16foot DW raft beds)(an additional 128 cubic feet of water, or about 958gallons of water, and 304 square feet of surface area to support denitrifying bacteria).

These are direct UVI system figures and formulas.

I didn't list ALL the components of my system in that very brief "introductory" post. And besides that.... read on.
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Now then, all that said, I never once said how many fish I was going to stock. I lurked here for quite some time. I realize many of you have real world experience in aquaponics, specifically with GBs. I almost didn't post here to start with because of how I see some members, very vocal members, jump to "you need to do more research", and "you need to use the search engine" instead of constructively answering questions, and without ANY knowledge of just how much research someone just might have already done.

So, do I need to do more research? Yes. I bet many of you do too. I could draw and label the UVI system in my sleep. I know about the clarifiers, complete with their live-in fish, the degassing, etc etc. I have done my research on that topic, and from other sources as well. Nothing in my original post even indicated otherwise. But I don't know everything... infact, my knowledge is admittedly limited. That's why I thought I would be able to ask questions here.

What I have seen from reviewing so many threads here is that many of you CHOOSE not to push your systems. You are comfortable with what you are doing, and that's fine because it's working for you. My system is an experiement. Plain and simple. It's goal isn't to become a huge commercial thing. It's an attempt to scale back a successful line of systems into someone "containable". A commercial scale clarifier isn't going to work for me... so I'm looking for options. Thus the questions.

At this point, without the benefit of experience, I have to rely on my research, and I've followed it to the letter. Do I honestly feel like DW beds alone will give me the surface area for denitrification? I have my doubts, but the UVI system works. Even so I probably will employ a GB or two just to feel a little safer. The question about the additional filtration was purely about more surface area.

So, I surely hope I can rely on this forum for constructive, supportive advice, and criticism when it's warrented. I value the benefit of your experience, but please give me the benefit of the doubt in respect to my own knowledge base.

True enough... the suggested stocking densities I quoted are just that ... a safe stocking density... related to flood & drain systems, particularly new systems... for people new to aquaponics... and with certain suggested filtration capacities...

And expressly noted that Tilapia could, and often are stocked to denisities above the figures suggested... particularly in RAS aquaculture systems... due to the nature and tolerances of Tilapia... and usually with considerable filtration and oxyganation that may not be apparant ... or stated

And, as mentioned... with a suggestion of a 2:1 growbed capacity:fish tank capacity... to cope with full grown fish and feed load...

It's often forgotten that even with a 2:1 ratio... of growbed volume... the actual filtration capacity is actually only about 50% of that total volume... the rest being that of the media itself...


Yes, and no... it's also related to your oxygen demand to provide oxygen for fish respiration, feed conversion and oxygen load due to other biological oxygen demand... i.e decompostion of uneaten feed and other fish wastes... bacterial conversion... and any micro-organisms in the water...

These values increase with fish growth..

While you didn't express any absolute value regarding stocking density... you did begin your post by stating that you intended to stock heavily...

It's also predicated on the complete, or near complete removal of solids from the system... and auxillary oxygenation of the raft channels... to supply the necessary oxygen demand...

And the oft forgotten... and sometimes un-stated... or under-stated continual water replacements...

My post was only ever intended to be constructive and a reponse to you questions.. as you asked ... and some of your questions seemed to indicate that you may not have completely understood the filtration aspects , particularly in regard to filtration... and the importance of solids removal in a UVI style operation...

Sorry but a 55gal bucket filter.. just isn't gunna hack it... IMO... and you asked...

Actually many have been pushing their systems of late... and many without understanding the basic principles and requirements... with the result... especially in new systems... of 100% fish mortalities

I would certainly hope you could rely on advise from the forum.... even if it times it might challenge your previous research or interpretations... and I'm all for experimentation...

Just trying to help...

To give you a concrete example of filtration requirement...

I have a 6000L tank... run strictly as a RAS system... (no growbeds, no rafts).... employing 3 x 210L drums as filters.. and two auxillary box filters....for solids removal and bio-filtration...

That's three to four times the filter capacity you suggested... albeit for about three times your water capacity...

Stocked with 250+ trout at an average bio-mass of about 250gm.... feeding about 4-500gms of feed per day...

Constantly monitoring pH, ammonia and water temperatures... with several years accredited aquaculture study behind me....

And I change out approx 3000L of water a week...

Because I'm approximately 50% underfiltered...

People here will try to help.
However, keep in mind that most of us here have most of our experience in Flood and drain media filled grow bed methods. So, we might not have the answers for you about how well a sock filter is going to remove solids and how many times an hour you will have to replace and clean them.

Some people here have experimented a little with swirl filters and other solids removing methods. I even did try a little in that line but I found that if you don't clean out the solids almost daily, the smell is enough to knock me off my feet when I do.

I have also learned the hard way that if you can arrange your system to overflow out of your fish tanks into your solids filters you will have much better luck filtering the solids out. IF you run the solids through a blender/I mean pump first you wind up with farm more fine suspended solids which are much harder to filter out. I have found that most any type of cloth or paper filter will plug up very very fast and probably need changing out/cleaning on a daily basis if it even lasts that long.

And please don't let RupertofOZ's tone put you off. He really is just trying to rescue you from making a big fish kill for your first experiment. Many people come on with a first post of something like "Hay I have these two pools and I've set up netting around them to keep things out, how many fish can I put in them." (then people go on to tell them they need grow beds or filtration before they get fish and that inflatable kiddie pools are not the best fish tanks) -next post- "Well I put 100 silvers in the one pool and they are all dieing after only a few days, how do I fix this" (people start asking about test kits and grow beds again.)

I have pushed the limits with tilapia before. What I found is that you need to pump lots of extra air in to keep them eating well. Yes I know they can survive very low DO situations but they won't eat and grow well under those situations.

Good luck with your experiment. Sorry there are only a few people on this forum with much DWC AP system experience.

However. I believe the next BYAP Mag will have an article about their commercial system which is DWC for the plant growing and from the sounds of it, the bio-filter/solids digested is relatively simple. I'm looking forward to hearing more details about it. That system uses more power for aeration than it does for water pumping.

Yep, aeration is definitely a key point in a system like this. As recommended, there will be a large air diffuser every 4 feet in the DWC beds. I will also have a venturi setup feeding back into the FT. There will likely be additional aeration in the FT. I said in my original post that I "had thought about having a sumpless system", but I know the benefits of having a sump, and will very likely incorporate one and have a CHIFT PIST type system. I had wanted to keep my FT relatively low to the ground, but honestly I'll probably have to elevate it to be able to keep it warm enough in the winter.

Even though this is going to be indoors, I have yet to decide if it's going into my climate controlled mother-in-law's quarters, or in my enclosed garage. I am worried about humidity in the outbuilding, and it's effect on the drywall and acoustic tile ceiling. I don't want to ruin a building doing this. All that said, it sure would be easier to maintain my temps in that building. Another plus is that nothing else is out there, so I would know exactly what my expense in running the system would be as far as electricity goes. A drawback to using that space would be that I would be forced to use a FT that would fit through a standard doorway, and as such might have to rely on a steel/vinyl clad pool. Finding a good FT in Arkansas has proven to be difficult. Was going to go pick up a polyethelene 9ft diameter round by 2 ft deep stock tank today, but it had sold this week. I did find a source for corn syrup IBCs($50 US but no metal cage, only cardboard box), but I prefer something with a larger surface area.

Any words of wisdom about the humidity issue?

We do have a few people running indoor set ups for winter time, they might be able to give in-site about the humidity issue.

If you take a look in my system thread, I have a tall tank roughly 700 gallons (depending on how deep I fill it, I started out calling it 600 gallons but now I'm filling it much closer to the top.) Anyway, look I think starting about page 80 of my system thread and there are pictures of it's construction. two cattle panels, some cable hardware to secure the circle, some insulation, a tarp, and a really good chunk of pond liner and I have a 700 gallon tank for a very reasonable price. I suppose this is a big tank that could be brought through a small door and erected inside though it would be a challenge if the space inside is really tight too.

So what kind of fish are you planning? Tilapia I'm assuming with your talk of keeping things warm.

Yes tilapia. I've investigated other fish and if I'm going to be experimenting, I think I'd rather stick to a hardier fish for now for sure. Tilapia always were my first choice anyway. Don't want to deal with trout and having to cool water... I can heat it way easier than I can cool it. Catfish don't really appeal to me... I wanted a white, flakey fish, and crappie are a no-go as far as culture is concerned unless I want to breed and raise minnows or mosquito fish in mass at the same time.

I did look at some hybrid sunfish, but unless you're going to harvest them at 0.5lbs (and I saw the thread about that), the growout time for a larger fillet is like 2 years. I spoke for quite some times with a fishery manager here in Arkansas about the various local species and their pros and cons. He did offer to give me up to a hundred of whatever I decided on, provided I gave him a report of how it went, but I imagine I'm going to stick w/ tilapia.

I can tell you that catfish and tilapia are yielding very similar for us. Actually the Catfish are yielding more but we buy them as fingerlings rather than breeding our own.

With tilapia, if you want to get high yields of 1 lb fish in under a year, you will definitely need to keep the water warm and you will probably need to get all male stock. If the fish start breeding, they don't grow nearly fast enough. Even caged so they can't breed, I'm not overly impressed by mixed gender tilapia growth. It might be just fine for a Backyard AP system where growing out lots of large fish fast isn't the primary goal but if you are trying to get max fish flesh out of an AP system, mixed gender tilapia are really no better than many other types of fish.

However, I know many people don't like catfish as much. I don't find the catfish and the tilapia to be all that different though in taste and the catfish is only slightly more dense but is still white and can be flaky. Perhaps it is because my tilapia and catfish are eating the same feed