Backyard Aquaponics
A place to discuss aquaponics

Researching on the fish side.

First High CO2 levels in the water can cause problems for fish.

see http://www.thefishsite.com/articles/103 ... quaculture

I havn't been able to find anything useful on fish CO2 production except this:

http://www.sciencedirect.com/science?_o ... 884362222a

However all the measurements of CO2 production from the fish, nitrification bacteria and heterotrophic bacteria are given in mg/L. Not really sure how that translates into calcs on the system as a whole. If the full article was available maybe it would say

One of these days I'm going to get a subscription to those academic websites. Its just too frustrating only seeing the abstracts.

And keep in mind that plants usually get their CO2 from the air, not through their roots.

A lot has been written about CO2 enrichment for accellerated plant growth. I have a few books about it myself. As I understand it, only the green parts need CO2 because only actively photosynthesizing parts are using CO2. The roots need Oxygen all the time -- dark or light. Also...it seems that any other deficiency will be aggrivated in an CO2 enriched atmosphere. Each plant responds in a unique way to CO2 enrichment.

Before enriching with CO2, I plan to measure the CO2 levels in my greenhouse -- the fish will be generating CO2 all the time. Speraneo mentions that as a huge benefit of AP. The cheapest CO2 systems use bottled CO2 and a regulator. Other systems burn Propane or Natural Gas to produce CO2. The best systems modulate the production of CO2 based on measured levels. CO2 levels above a certain level can pose health risks to humans (fish too, probably).

I suppose another risk that could be associated with bottled CO2 in an confined growing space would be excessive levels of O2. In a closed greenhouse, available CO2 is rapidly depleted and then photosynthesis stops or slows to a crawl. However, with CO2 enrichment, photosynthesis could theoretically continue producing oxygen until oily substances would spontaneously combust. That is one good argument for using burners or fish (or rabbits or humans...) to consume oxygen at the same time as producing CO2. I've read that slightly elevated levels of O2 can be very healthful.

Good luck. if every aquaponicist wands a DO meter then a Co2 meter is the holy grail

from memory they use a specific bandwidth of IR light in the sensor as both CO2 and water vapour absorb IR light.