Backyard Aquaponics
A place to discuss aquaponics

I've heard the opinion of Tailor made before, that you cant just recirculate the water bceause among other things that the pH requirements for the fish and plants are significantly different. Now it may be true for bara but for the fish species that we are considering for our system Ive been told it wont be an issue.

It is a free service Stuart and is supported free of charge to users. The forum and its off track posts are the nature of the beast I'm afraid. Sometimes people don't understand what goes on behind the scenes making the forum available.
If you want a thread sustainability and density why don't you call it that and copy/quote the relevant posts yourself

Sorry Faye I know that the mods do a lot of work running this forum, had a bit of a chat with Jaymie about that when we saw her recently. I wouln't have asked except that Ive seen others ask and have their request granted on a number of occaisions. If people are too busy thats fine after all it was request not a demand.

As to starting a thread on sustainability and density thats what this thread was meant to be

Apologies if you feel the thread has been hijacked Stuart, but I must point out that you raised the issue of sustainability in your opening post by making the ambit claim that higher stocking densities resulted in low embodied energy costs per kg of fish. So perhaps you hijacked your own thread?

Stuart, have a look at a chat with Lennard about commericalisation of aquaponics... it also includes links to both the sizing tool and the pdf which explains the basic underlying formulas it's based on...

It will enable you to download the tool as an "editable" version.... allowing you to input your own numbers....

http://www.ecofilms.com.au/2011/01/08/d ... quaponics/



That's not really true Stuart... the tool is designed for used with both media based systems and UVI style raft systems...

And Lennards initial experimental work for his thesis was basically a flood & drain model...

Followed the links and that article has good points I'm pretty sure that it was posted to the forum some time ago but still worth a reread. I couldn't find the editable version though and while the pdf describes his thought process it dosn't actually give values and formulas. He does say that he has recalibrated published UVI data but not how and by how much, without knowing this I cant make an assesment on the validity of his asumptions, techniques and approach. There fore it is not something to rely on but then Wilson states a number of times that at best it is only meant to give general guidelines for backyard systems and for specific systems especially commercial systems a specific design needs to be done. Thats what I've been working on.

As to Wilson's orginal work I thought that his system was based on a constant flood model and that he used extensive RAS equipment in addition to the constant flood gravel beds.

Its not the PH requirements for the fish that matters most its the biological bacteria in the filter, with 7.8 being ideal.

It's long been held that pH 7.8 is the preferred pH for bio-nitrification.... but no explaination could be provided as to why bio-nitrification could operate almost as efficiently between ranges of 6.0 - 8.5....

But this was always based upon the accepted view that nitrobacter were the principle nitrifying bacteria...

Recent research has shown this long held view... to be WRONG.....

It is in fact nitrospira that is responsible for nitrification.... and capable of doing so within a wide range of pH values....

As seen in aquaponic systems....

Similarly... there's considerable doubt as to the validity of suggested pH values reagrding fish growth...

Again, particularly in Australia.... fish have been seen to not only survive, but thrive ... in pH values from as low as 5.5 - 8.5....

Much of the accepted ph values oft quoted.... are probably more a reflection of the nature of the pond based aquaculture systems.... preparation and maintanence of algael bloom techniques....

Rather than any total effect of pH alone.... indeed, some of the benifit of the suggested values probably have as much to do with "hardness"... and sceletal development... rather than any natural pH preference....

Huh Well there you go.

Dont a lot of the south american water conditions end up in the acid range. I seem to remember that all the amazon fish I used to keep Tetras, discus and the like preferred a low pH.

Nitrospira is the newly discovered bacteria responsible for Nitrification but still needs a higher PH to work at maximum effiency http://microbewiki.kenyon.edu/index.php/Nitrospira

You can run a system with low PH, but can you stock the same number of fish as a system with higher PH?

I am sure Tailor made have done a lot more research and trials than most people on this forum, so I think I will trust their judgement.

The information on the pH I got was from a range of RAS sources none of which were experienced in the production of Baramundi. The information I got was for perch, salmonids and a few other fish I don't remember. So for Bara I couldn't say but then I'm not going to be growing bara so I havnt done the research.

There's no reference in the link quoted... to pH... let alone any requirement for a "higher pH".... other than a note that system water that is too "rich in ammonia or has a pH that is too low will inhibit Nitrospira's nitrifying activity"... something which we are already well aware of...

The link above is a condensation of the original work by Hovanec, and referenced.... here's the direct link to the paper.... http://aem.asm.org/cgi/reprint/64/1/258

I've got other bookmarks on the subject that show nitrospira will work effectively in pH ranges from about 5.8 - 8.5.... with reduced effectiveness at both ends of the scale...

Personal experience, and that of many other peoples AP systems... would seem to support this theory...


As too the pH requirement for fish growth... as I said, and Stuart noted.... much is based upon Rowlands work regarding Silver Perch (any other species).... in pond based aquaculture....

Yet in nature.... most Australian species survive, and thrive... in pH ranges well outside those recommended in pond based aquaculture...

I say again, I believe this is due more to suggested "hardness" values... and calcium availablitiy for skeletal development.... again, many people can demonstrate perfectly acceptable growth rates in aquaponics in pH ranges well outside those quoted...

And in RAS.

... which tends to support the belief that much of the "recommendations" ... are more applicable to pond based aquaculture...

I would like to see those, all the info I have found so far like thishttp://www.thewaterplanetcompany.com/docs/WPC_Nitrification%20&%20Denitrification%20.pdf suggest otherwise?
I know the nitrification process will work at a lower PH, my system has been running at 6.4 for the last few months, although lightly stocked at the moment, the point I am trying to make is the effect on stocking densities PH has. Can you stock more fish in a system with a PH of 7.8 compared to the same size system running at 6, and if so how much more?