Constantly spiked Nitrate?

Not many. Some of the damsel family, some of the smaller octopusses, gobies, some frog fish...
 
Hippocampus zosterae

The only marine fish that I feel comfortable keeping and breeding in a pickle jar.

Hippocampus zosterae would be lose in anything much bigger than a 15 gallon tank. Very invert-friendly (unless said invert is a very tiny arthropod). And they are as prolific as freshwater mollies.
 
Its a tank bred small blue tang, about 1 to 1.25 inches in length. It's actually smaller than most of the clown fish i have seen. As soon as I notice it getting too big for the tank I plan on transfering it to my brothers 150gal. I've had the fish around 1-2 months and haven't really noticed any size change, so I'm guessing it'll be alright in there for a while.

Any other suggestions regarding the NO3?
 
If it isn't growing, it's being stunted, either by the tank size, malnutrition, or the water conditions. Sorry. Very few fish are slow growers throughout their life. Most grow very fast the first 6 months, then slow down. For SW fish, this isn't the case--most grow very fast to their adult size, and then only put on 'weight' as adults, not getting longer of taller, just heavier.
 
The owner of the small LFS where I bought them said he had experienced the same thing. He had a school of these blue tangs in his 100gal for a month or two and they didn't experience much growth either.
 
A school in a 100 is a different situation, with the same result. The fish will inhibit each other's growth.
 
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