Backyard Aquaponics
A place to discuss aquaponics

BB,
Yeah, I'm still good on working something out, I'm sure we will work something out. I like the idea of the silver perch,
I always planned this brew of trout to be in a larger system with about 1000l of GB, just i haven't finished it yet (sounds familiar )
One of the AP books i have, say that 100L of GB can maintain 3Kg for fish and can go higher with a larger FT. Also every fish needs at least 10L water min. so with these ideas in my head I though I was cool for a month maybe till the fish got to maybe 6-7 Kg total weight. Anyone can comment if I have my wires crossed. I do realize that its not enough for so 50 - 500g fish, but hoping that its alright short term

regards
Matt

Matty, I think 3kg per 100L growbed was the absolute maximum... I think a thread recently highlighted that this is not really a safe area to be in...

http://www.backyardaquaponics.com/forum/viewtopic.php?f=12&t=6646&st=0&sk=t&sd=a&start=15

Nope... the initial suggested ratio was... 3kg of fish per 100L of fish tank volume.... with a corresponding 2:1 ratio of growbed volume

i.e... a 700L fish tank... with 1400L of growbed... and 21 kg of fish... maximum

Somewhere it became common place to run systems on a 1:1 fish tank volume to growbed volume... while still maintaining the same stocking rate...

At virtually the same time... it also bacame commonplace to double the stocking rate... on the premise... that the fish were small.... they grew at differing rates... and that people would start eating them at around 500gm... rather than growing out to 1kg...


In essence... people doubled the stocking rate... while halving their filtration....

A fundamental error ... IMO... and one that means that most systems are always on the edge of disaster... especially when "new".... and especially when the limitations of filtration and oxygenation are approached... usually around 500gm...

Just when people might be thinking of harvesting some fish...


Most fish actually grow at a very similar rate... sure you get the odd runts...

Fast growing fish... like trout, or Barramundi.... require linearly increasing feed rates... hence linearly increasing oxygen demand and filtration...

That's why myself, Joel and others recommend stocking to your filtration capacity... or as Joel sometimes expressed... fish per growbed ... typically a growbed is 500L

Thanks for straightening this out for me, I'll have to get one of the other beds on line pronto by the looks

regards
Matt

measured my PH in the morning just to make sure that it wasn't algae which caused my swing, All OK at 6.8
todays reading,
Am - 0
rites 0 - .25
rates 10 - 20
PH 6.8

trout smashed the feed tonight, gunna go easy on the feeds till i get at least another bed going on the weekend.
matt

Thanks Rup, that really does straighten out the old ratio debate. I now understand why the suggested GB:FT ratio is 2:1. My system in its (final) configuration would be 1:1 at best and hence my tentativeness towards stocking too many fish. I do realise I will need to offload some SP to be able to handle some trout but I'll make those decisions once the system is complete. Untill then no trout for me I think.

You will still need to go easy on the feed until the new growbed has bacteria established... takes a while in the cold weather...

For Rainbows 24hrs at ph of 3.8, Browns can even go a little lower. You shouldnt get any deaths until your ph was below 5 and most likely below 4.5.



Thats only because you are buying fish that have already been graded Rup. Some of my Silvers from last summers spawning are still only 20mm whilst some of their brothers are over 100mm. I'm not just talking about the odd runt as I recon I would have around 1/4 of the fish under 40mm. When I sell these fish I dont sell 20mm fish with 100mm fish just because they are the same age, there all graded as you would expect therefore getting a batch of fish of a similar size that should hopefully continue to grow at similar rates.

True enough Gavin... but most of the fingerlings people will buy are generally pretty uniform...

And the comment was more a "reply" to statements made by others "that fish grow at different rates"... even though the above is usually the case...

Other than Barramundi smaller than 100mm... which require grading.... Silver Perch are certainly the species where I've noticed the greatest difference in growth rates... and possible differences when supplied...

As a newcomer reading this thread and the link to here from Mattys first system thred has been informative. I do feel at this moment like an inexperienced person asked to conduct an orchestra. Baton in hand, opening the first page of the music score and seeing the 25 orchestra instrument section musical scores.
However, at age 65, I can look back on a number of complex challanges and outcomes. Occupational challanges, military challanges, endurance tests, fraught with initial failures. Stubborness, and patience sometimes resulting in some success.
My complements and gratitude to those who so readily and thoroughly share.
Dennis
Oldandfound1

To comment further on the stocking rate issue.

Most of us are trying to get away from giving the "MAX" stocking numbers anymore.

For something like the BYAP systems with the 500 liter grow beds, people are generally told to stock between 20-25 small fish per grow bed as a recommended stocking level and the system can cycle up as the fish grow. That would assume a harvest size of about 500 grams.

If you go stocking near the "MAX" with a new system while trying to add more grow beds, you are really running a risky challenge and I hope you have lots of fish keeping experience to avert disasters.

In imperial measure we have been recommending stocking 1 fish per cubic foot of grow bed media, assuming 1 lb grow out (if you are going to stock something like catfish that you want to grow out bigger, then stock half as much or harvest half of them small so the other half can grow bigger.)

Even those recommended stocking levels could be a bit high if anything is not going smoothly in the first season of a system.

I agree with what everyone is saying.
So far I've been very vigilant in regards to keeping and eye on the amount of food input and toxicity levels every day. I agree there is little room for error with this ratio. thing could go south real quick and can only recommend the the ratio mentioned above as the best ratio because you have a bit more of room to breath or time to act.

Regards

matt