I only watch my nitrate levels and any leaf yellowing. The plants will let you know.
Unless someone like you cares a whole awful lot, nothing is going to get better. It's not.-- Dr. Seuss, The Lorax
Simplicity of character is the natural result of profound thought~fortune cookie
I'm with Stucco. Watch the plants. If you must test, pH and Nitrates and calcium hardness are what is important to plants. You need to strike a balance between what the fish need and what the plants need.
A few years ago I aet up an aquaponix system. It didn't work. I had too few fish and too many plants. I had an eight foot pool two feet high with six 4" koi and 4 4" gold fish going through a 4'X8'X6" deep grow bed. The plant didn't grow very well, but the water coming out of it had lower nitrates than the tap water used for the pool.
This time, I want to set up a system that I can easinly move from the greenhouse to my workshop in the winter. I now have minnows that I have been growing for a couple years. If I can't solve a couple issues with the minnows, I will have to switch to other fish.
I have a mix of rosie reds and wild minnows. The issue is, that if I want them to reproduce, I don't want the fry to get caught up in the system. I could try a spnge on the inlet of the outgoing pump, but then it might plug up often. Or, I could section off an area with a fine screen. Just not sure yet.
i'll be interested in your progress with the rosy reds.. i've been puzzling over that myself as i have aroudn 30 or 40 rosy's in one of my tanks.. thinking i'll section the 55gal tank, and try to find the eggs when they happen and move to their own little area.. but from what i've read, the male will protect them for a while..