Backyard Aquaponics
A place to discuss aquaponics

...is it as hard as finding the right type of household ammonia? I.e. Do i have to make sure it is pure urea? Do I need to watch out for other ingredients such as additives? Or is urea as plant fertilizer usually sold by itself?

you will want to look at the list of ingredients or if there is a chart showing what other minerals are in there. I know others have used urea and I have seen a picture in one of the threads of the analysis. Even plain urea is likely to have some stuff that we don't want to overuse in our systems. I don't know where best to get such fertilizer in small quantities on this continent though.

Now if there ended up being toxic additives in either the urea fertilizer or household ammonia (say the surfactants) that I used for the cycling, if the fish survive for months then that would be a pretty general guideline to indicate that the plants (not the fish) would be safe to consume, correct?

If you are only cycling up with the additive and it is a small system, I doubt there would be enough in the system to cause you issues.

Now if you were to run a completely fishless system and eat only the food provided by the system, then you would need to be far more worried about any heavy metals in the fertilizer. Lead would be the primary worry in such a situation.