Out here everyone is allowed to send their tap water in for testing once a year at your municipal water. Worth checking to see if you also have that available to you. You get a spread sheet of everything from your sample. If not yeah, a university student or something can help you. I think you've got a lot of biological media going on which is good. More the better. But it's worth maybe investing in switching out the bioballs with seachem matrix which never needs replacing either. I see it for $25- @ kensfish.com for 4liters of it. It's way more efficient then bioballs, easier to clean when actually needed. The polyfill is good too as addition, i've used that for years. I always preech to never use carbon, but in your case it might be needed for now, or some purigen. Keep in mind too carbon is really only efficient for a week, literally after that you can run into it causing issues.
A lot of your issues i've seen with people with well water, there is definitely something not right going on with your municipal water. Maybe it is good at the source where they are testing it, but there's a lot of distance between them, and your house, thats why i suggest having your tap sample tested. For your nitrates to sky rocket like that is usually too much bio-load but with your water change schedule, and amounts, your filtration, the plants that almost rules that out completely. Mine is stable at 5-15 max ever, 150ppm is insane :/
A lot of your issues i've seen with people with well water, there is definitely something not right going on with your municipal water. Maybe it is good at the source where they are testing it, but there's a lot of distance between them, and your house, thats why i suggest having your tap sample tested. For your nitrates to sky rocket like that is usually too much bio-load but with your water change schedule, and amounts, your filtration, the plants that almost rules that out completely. Mine is stable at 5-15 max ever, 150ppm is insane :/