Breaks down completely? Or is 24 hours the half-life? Or is 24 hours the time it takes for plants to take-up the product from the water column? Or is 24 hours the time it takes for the glutaraldehyde to oxidise to a still-usable five-chain carbon molecule, glutaric acid?
A lot of assumptions, but nobody with a mass spec......
Yeah, that's why I used the term "It is said"...
However, every time I've heard "it said", the assertion was that it broke down completely within 24 hours, and there was absolutely no carbon enhancing activity left...
I've even asked the question if anyone had any evidence as to which breakdown mechanisms are the prevalent ones in aquarium tanks... only crickets could be heard in response...
Clearly there's a lot we don't understand about glutaraldehyde in aquarium use.
Digging around in this thread:
I found a link to an article about glutaraldehyde breakdown in river water:
It gives the half-life of glut as 10.6 hours in aerobic river water, 7.7 in anerobic river water. However, sterile water caused no appreciable breakdown except at extreme pH over 31 days.
So, it is reactions with organics and/or living organisms that cause the breakdown, but I think we all knew that.. the half-life numbers are new to me.
Assuming our tank water is anything like aerobic river water, then we should see a 10.6 hour half-life.. In actuality, our tanks may be considerably more bio-active than river water, as the density of fish and bacteria is going to be higher.
Regardless, sticking with a 10.6 hour half-live would suggest that after 24 hours we are decayed by more than 2 half-lives, and about 20.8% of the original dose remains in the water after 24 hours. However, that's only the breakdown of gultaraldehyde into glutaric acid..
According to this MSDS:
Which quotes the same 10.6 hour half-life for glut to glutaric acid, but also says the glutaric acid is completely metabolized within 48 hours...
So, perhaps 48 hours is a better life-span for the CO2 producing effects of Glutaraldehyde/excel/etc than 24 hours...