Backyard Aquaponics
A place to discuss aquaponics

We know you guys are Faye - and I think I can speak for the majority of the forum members and say that we do appreciate it !!

Another rule of thumb..... level your system before/as you build it, not as an afterthought.

And I'm still trying to figure out where people heard the rumor that beneficial bacteria prefer dark places. As far as I have learned, they thrive throughout the entire system wherever water touches including growbeds, inside piping, on items in the tank (pumps), and fish tank walls (which are not dark). That is the slime feel when wet.

2kg/100L = 1lb/6 gallons

7.5 (roughly) gallons per cu ft.

So that's what, 5 fish for every 4 cu ft? Meaning that for an IBC that is roughly 16 cu ft you can run a recommended level of 20 fish per grow bed (assuming you let them all get to 1 KG). So 60 fish isn't a bad thing for a full system.

(when I say full system, i mean 1 IBC for the FT, and 3 grow beds each 16 cu ft). Like the tote system from Murray's dvd.

For a newby an ibc system 25 fish is max i wouldent go over 40 and thats cutting it fine just because you have 20 sq meters growbed doesent mean you can put 60 fish in an ibc

How did the 2kg/100L GB formula come about? Is it calculated on the amount of waste a 1kg produces or from experience or both?

These figures came about through lots of different systems being run over time, and debate amongst the many members to try and find recommended levels that people could stock at safely.

The figures are roughly based on a media bed of about 30cm (1foot) depth. One thing to try and keep in mind is that it all boils down to feed input vs No. of plants extracting nutrient.

I'd be looking at stocking more like 30 fish in a system like that, and that's allowing for them to get to 500g, not 1kg...

Yeah, you're right Thorn - I've seen a good dozen or so moving-bed biofilters and they were exposed to daylight and working extremely well.

Keep in mind that the moving bed bio-filters are not exposing the bacteria to strong sun long term. All systems have some surface areas that are growing bio-filter bacteria that are in the dark (like inside pipes, in the gravel beds, etc.) Some of the bacteria is more prone to being inhibited by light than other bacteria. For instance, the bacteria that converts ammonia to nitrite is slowed down by sunlight, you can slow down a nitrite spike by taking some of the rafts off of a DWC system for a while until the bacteria that convert nitrite to nitrate catch up, then when you put the rafts back on the ammonia conversion can catch up again and the system finishes out cycling.

Now we must be sure when we explain the stocking rules that people understand it is the filtration number that is being rattled around. Saddly people often mishear the numbers and wind up with twice as many fish with half the amount of filtration, or worse yet, get a bit tank stock it with fish and never even a thought to any filtration (they seem to think they need to build up the waste before there is any reason to add a grow bed, unfortunately all their fish tend to die before they ever get around to it and they then blame aquaponics for killing their fish.) Sigh.

1 fish per cubic foot of grow bed (growing that fish out to 1 lb) is an easy number I like but if you are not going with square feet of grow bed at 1 foot deep, I've actually been stocking by gallon measure where I have 100 gallon grow beds. So going by gallon measure. I will stock 1 catfish per 10 gallons of fish tank with 20 gallons of grow bed filtering for it. I will stock 1 bluegill/tilapia per 5 gallons of fishtank with 10 gallons of grow bed filtering for it.

In imperial, I'll simply follow BYAP's recommendations of 20-25 fish per 500 liter grow bed with the planned harvest size of 500 grams.

The recommended pounds of fish per system volume seem to be right on with what I learned about high density fish culture on my farms. I raised Koi which is just a pretty carp and they are a high volume eater and pooper so filtration is the key. I developed and used several types of filters but the best was a stream filled with plants, specifically water iris. Thorn made a good point that in a properly setup flow through system everything under water becomes surface area for the nutrifyiing bacteria. It just requires a good flow of water, you can tell when its right by feeling the walls if they are slicker than greased owl poop then things are good. Dark of bright sun doesn't matter.

My sales houses had two 4' x 40' x 2.5' troughs with an isle down the middle these held about 3,000 gallons each. Connected on the outside was a 40' x 2' x .75' stream filter the fish trough and stream where looped together forming a circle. I grew the iris bare root in the stream. Each trough had on average 300 fish I had a 3 inch PVC pipe with holes drilled in it on the bottom running the length of the trough. The koi were divided into 5 suspended cages about a foot off the bottom under them were 4 large 24" albino channel catfish which I called the street sweepers. Since my focus was on the fish I could have a 5 to 1 volume ratio FT to GB. That would not be much good in the Aquaponics world who want a balance of fish and vegetables, so what is an old fish farmer to do? I know two streams - one for iris and one for vegetables.

So the recommendation of one fish per ten gallons is a safe goal in my opinion - I like a 3 pound fish to fillet for the wife and my dinner.

So for 1000ltr ft & 800ltr gb with a flood & drain syphon system, and Barra apparently growing to 1kg in 12 months that would mean you consider 16 fish to be a safe level?

Shouldnt this thread be called Oft repeated Rules of Toe

upnorth - yes
larry, have you got anypics? that sounds interesting set up!

freoboy, I will make a movie today of my system. It is 3,000 gallons and has over 300 fish which are 7 to 10 inches at 5 months of age. I have a 16' stream filter and 2 grow beds. I guess I'll post it in the members systems thread.

Great, I look forward to it