Wasn't trying to ask a "smart ass" question :) The reason I asked about the paper was that I could not remember the levels off hand, just new that they were higher. They went over 50 mg/L in their rafts. Here is the paper for those that are interested.
Sylvia Bernstein said:Hi Kobus. I haven't read UVI's literature, I"m chagrined to say, and far be it from me to question such esteemed work so I'm sure they are right. I'm reporting what I've learned through my own system, and going for the notion of balance. While the system may be able to survive very high levels of nitritate I wonder if it is best for the long term balance of the system - feels out of whack to me. Like I said, I've always run at about 5 - 10 ppm with my 12" media beds and everything grows like gangbusters. If it goes below 5 I figure I need to add more fish. But this is certainly less scientific than UVI...but also a different growing method with more bio-filter...
Nice reference Kobus, thank you. In your combined system, what readings do you shoot for (and what do you get)?
Sylvia, I was basing my estimation of nitrate levels on what Murray Hallam had mentioned regarding when it's time to add an additional bed. I believe he said that if nitrate readings are consistently over 300 ppm another bed is needed. I made what seemed to me to be a simple logic leap, and assumed his regular numbers were somewhere approaching that level (silly to make any assumption, I'm chastising myself as I write this) . I may have spoken too soon regarding stocking levels as well, your breakdown of stocking density is more detailed than my quick estimate, and is most likely far more accurate.
I didn't really comment on it before (and because you have tilapia which are pretty bomb proof it is probably no worries anyway) but I don't like to see measurable ammonia or nitrites in my systems. I grow catfish which are more sensitive to water quality though. If ammonia or nitrites get up to .25 ppm I start looking to see what might be wrong with my set up since seeing ammonia or nitrites usually means a build up of something or that the bio-filters are overloaded.
Since you say that you just changed things around and that you just added a grow bed, then I might guess that to be the cause of the ammonia and nitrite readings but if they don't go away, all the more reason to eat some fish soon.