I have found a liquid chelated iron and zink compound at Home Depot. I am hoping this will help improve the results in the system. Our tomatoes and peppers are small and sparse at best. There is some yellowing in the plants, but not real bad. Generally the growth is slow in all of our plants. Our seedlings start out good and then peter out. The pH is 6.4 to 6.6, NO2 is 0 ppm and the NO3 is at least 60 ppm. The ammonia hangs around .5 ppm. The catfish are happy and growing well. Our system is not quite 5 months old, but it seems it should be doing better than it is. Now, if I use this chelated product, I am not sure how much to put in the system. Thank you in advance for your help.
I did not purchase the iron/zink from my original post. After some searching we found chelated iron at a local nursery supplier. My wife spoke to the manufacturer and explained our goal. He recommended 1 cup every 2-3 weeks, for our 1000 gallon system, and so far that seems to be doing the job.
Thank you all for your informative responses.