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PostPosted: Jul 16th, '17, 10:26 
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Still new to the world of aquaponics, and have a small scale system ready to go for a dry run however. I noticing a lot of numbers and ratios and trying to interpret them is alittle tough. The most important number from my understanding is your amount of feed. Is that correct?

My small starting system is approx. 80-90 gallon fish tank, with a grow bed that can hold (I think) 70 gallons. It is roughly 2ft x 4ft x 13 inches (deep). From my understanding from all the ratios and equations, I can have 10 pounds of fish. but the most important number is how much I feed my fish based on the area of my grow bed.

Am I on the right track with this? Any clarification will help. Thank you


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PostPosted: Jul 16th, '17, 11:54 
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Hi Firemoose.

The volume of wet media in your growbed is more important than area. And it's probably easiest to work on weight of fish (when adult) rather than feeding volumes (which will change with type and age of fish and season).

There's a rule of thumb which suggests starting with at least 25 to 30 L (approx 7 gallons) of wet media in your growbed for every plate sized fish (See Mr Damage's post below) of fish stocked (when grown to adult size).

Not sure how much of your growbed will be wet but you should easily be able to stock however many fish will eventually grow to 10 pounds.

I don't think most backyard system owners calculate their feeding quantities too carefully... suspect it becomes important mostly in large and heavily stocked systems or commercially. I've always just fed my fish what they'll eat in a few minutes... a few times a day for fingerlings and once or twice a day for adults.

The other ratios that I think are important when starting out are that the grow bed wet media volume should ideally be as big as the fish tank volume (you're close enough) and that the fish tank volume should ideally be turned over at least every hour.

But don't get too caught up on the numbers - if you stock conservatively, you should be OK.

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Last edited by Dangerous Dave on Jul 16th, '17, 13:00, edited 1 time in total.

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PostPosted: Jul 16th, '17, 12:22 
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Thank you Dave

That helps a lot. Those are some simple numbers that I think will get me started. I am hoping to get my starting system started this week. I know you are suppose to cycle for a month to get the appropriate water levels ( which is a whole new topic) before putting in fish.

I was also thinking crayfish because they are SO abundant here in Arizona. Not sure how that affects how the system is run. Will be building a 2-3 IBC tote system hopefully this month too.


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PostPosted: Jul 16th, '17, 12:54 
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Three most important rules of thumb:

(1). Wet Gravel:Fish ratio

For the slower growers, such as Silver Perch (12-18months from fingerling to harvest), you need 20L+ of wet gravel per fish to safely get them to a plate size of 500gm.

For faster growers, such as Trout and Barramundi (around 6 months from fingerling to harvest), you need 25L+ of wet gravel. Even at that rate many people find they start getting Ammonia readings towards the end of Trout season, as Trout can easily get up around the 600-700gm mark in the 6 months... and they eat a lot.

(2). Gravel:Water ratio

The widely accepted ideal balance for a home based AP system is 1:1, but you can successfully operate a system with Wet Gravel:Total System Water ratio as low as 0.5:1, and up to 2:1.

If the system is fully stocked with fish to the Wet Gravel:Fish ratios previously mentioned, then the 2:1 Gravel:Water ratio will see your system very densely stocked with fish, which can be an issue for water quality, dissolved oxygen etc, which can become a really big issue very quickly in the event of a water pump or air pump failure.

Most single IBC systems run a Gravel:Water ratio around 0.6:1 (ie: 300L gravel GB over a 500L FT) and operate very successfully.

(3). Gravel Depth

A gravel depth in your grow beds of 300mm, flooded to a max level of about 250-260mm. This allows a good fish stocking rate per square metre of GB surface area, providing a suitable amount of nutrient for most commonly grown vegetables. Shallower GB's means less fish, so therefore less nutrient per sqm of GB.

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Last edited by Mr Damage on Jul 16th, '17, 12:56, edited 1 time in total.

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PostPosted: Jul 16th, '17, 12:55 
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Oops... have edited my initial post in light of Mr Damage's advice immediately above. I said stocking ratio of at least 20 L of wet media per kg of adult fish but looks like this is pushing it... Mr Damage's 500 grams advice is no doubt better for beginners and my experience pales in to insignificance cf his.

It might not take that long for your system to cycle. Depends on your temperature. You can even cycle with fish from the beginning, as long as you stock and feed lightly and check ammonia and nitrite regularly.

I'm sure you'll get some feedback from our Aquaponic Americans about the crayfish. Some Australians keep yabbies in Aquaponics... our version of freshwater crayfish. But they are very territorial/eat each other and I don't think they're a good way to get a meal of seafood with your aquaponic greens.

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Last edited by Dangerous Dave on Jul 16th, '17, 13:04, edited 1 time in total.

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PostPosted: Jul 16th, '17, 13:01 
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Thank you Dave and Damage.


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PostPosted: Jul 16th, '17, 17:17 
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Even though bluegill would be considered a slow grower they do eat a lot and I'd probably put them in the fast grower category for how much filtration they need.


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PostPosted: Jul 16th, '17, 22:31 
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Thank you Scotty.

So in a normal IBC flood and drain system. What additional filtration steps will be needed? Swirl filters?


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PostPosted: Jul 17th, '17, 00:10 
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If well designed, a backyard scale system doesn't require mechanical filtration, unless you plan on running a floating raft bed as part of the system. Many experienced AP'ers have run systems without mechanical filtration, for many years before the GB's required cleaning out... 5-6 years is not uncommon.

Ammonia, and the Nitrate it's converted into, are soluble in the water and constantly being created, all other nutrients in the system are mineral elements and come from the fish waste solids. So if you plan on running mechanical filtration, ie: Swirl filter or Radial flow filter, it will remove those mineral nutrients. Ideally the solids should be collected from the filter and treated in a mineralisation tank, freeing up a good portion of those valuable nutrients, which can then added back into the system.

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PostPosted: Jul 17th, '17, 00:40 
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Mr Damage wrote:
If well designed, a backyard scale system doesn't require mechanical filtration


What he means to say is that it doesn't require any additional mechanical filtration. The grow bed provides some by trapping at least a portion of the solids and breaking them down. The grow bed also provides biological filtration.

In a normal IBC flood and drain system that uses a grow bed and that is appropriately stocked you won't need any additional filtration (mechanical or biological). DWC and NFT beds are an exception because they need to have suspended solids removed. Assuming you don't have either of these, The IBC of Aquaponics (from BYAP) will give you a good idea of what's appropriate stocking, you can download the free PDF here - http://ibcofaquaponics.com/


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PostPosted: Jul 17th, '17, 01:42 
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I said exactly what I meant to say.

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PostPosted: Jul 17th, '17, 03:52 
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Sorry to put words in your mouth then Mr Damage. You must mean something other than what I thought you did with the term mechanical filtration.

To me saying that a grow bed doesn't provide mechanical filtration makes no sense. Sand filters, bead filters and gravel filters are considered types of mechanical filters (not their only purpose in most cases) and grow beds are a type of gravel filter. It isn't just about the particles being sieved out by the size of the spaces it's also about them being intercepted by the rock or being slowed down to the point that they settle or they become stuck to the bio-film where bacteria can break them down.


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PostPosted: Jul 18th, '17, 02:34 
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Thank you guys for your input. So I should have to need additional filters for solids if I am doing a flood and drain with clay medias. I have also heard that worms can help break down the solids too. is that true?

Got my small scale up and running. 100 gallon tank and 70 gallon GB (60 Gallon wet media calculated). Got it cycling with a single bass in the system. When should I start monitoring the water?


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PostPosted: Jul 18th, '17, 07:36 
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You won't need additional filtration if you're using a media bed and are stocked at a reasonable level for the size of your media bed.

firemoose529 wrote:
I have also heard that worms can help break down the solids too. is that true?


Yes. They probably also keep areas from becoming anaerobic.

Start monitoring right away and get a baseline for what the water started out at. Some water has nitrates to begin with and you want to know whether the nitrates you're seeing came in with the water or were processed to become nitrates by the bacteria in your grow bed. It will probably be one to four weeks before the cycling starts but you'll need to monitor regularly during that period so you know what's happening. You may see the ammonia climb before that.


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PostPosted: Jul 18th, '17, 07:38 
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Oh ok, I will start monitoring as soon as I get back home from work.


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