Sounds like it's still in the beginning stages of cycling. Minnows don't give off too much ammonia so it might take more time. I've seen it take up to seven or eight weeks went cycling with us. Good luck
I would rearrange the whole thing that way all the fish think they are in a new tank! But remember, the two sets of male female combo, are going to be really aggressive when when they spawn so have a back up plan sounds like a fun tank in the making!
I'm very surprise, with the fish you have now, it's a peaceful tank. As long as you have a back up plan if it doesn't stay that way, add a few more parrot fish and your flower horn. Are you at JDs male female? Because their temperament will definitely change if they breed. The same with your...
I've never tested our tapwater, but it is well water, and I just make sure I acclimate them over a longer period of time. And I agree, lots and lots of hiding spots and overstocking helps keep the aggression down to just one or two. My favorite kind of tank!
Once the tank has cycled properly, the nitrates will be more controlled as it will be used for the food to keep the bacteria going. Once it's fully cycled , The tank should have no problem processing 40 ppm of nitrates provided you're not overstocking or over feeding
If you have enough fish food left over that it's getting "White and fuzzy", you're probably over feeding. And yes it will cause high nitrates and I would do a water change. And if your face was covered in fungus, it's been there a while too! Probably not the healthiest diet for your other fish...
Mine have them daily as well as beef heart, shrimp, flake, pellets, vitamins, and other vegetables that I mixup in the blender. Then add clear gelatin and freeze in the little cube tray and use that as your main food! So much cheaper and much more healthy