Sorry it took me a minute to reply, but I did a little more research, and I think I have found a root cause. Sorry there's too many replies to quote, but to hit on the points: The tank is planted, there are 5 medium sized plants, and two small bunches of java moss, but in my research, I learned that with the exception of the java moss and a hornwort, my plants are all slow growing root feeders, which means they're not really capable of handling this kind of nitrate load. I will need to get some fast growing water column feeders, and an additional light bar so there's enough lumens to support faster plant growth.
I believe the culprit for my never-ending bacterial bloom (and high nitrates) is the water from my tap. It leaves the tap reading between 1.0 and 2.0 ppm ammonium. Using Prime doesn't help because one of its functions is to convert ammonia to the less toxic ammonium. Regardless, ammonia or ammonium, it's still eaten by the nitrifying bacterias, eventually converting it to nitrate. I think you can see what's coming...
Every time I'm doing a water change, I'm adding a huge hit to the bioload by adding a ton of ammonium and giving the bacteria a huge feast, and boom! in 2 days the bacteria have grown, and the nitrate levels are too high again, and I risk fish death or disease if I don't change the water and... well the wheel keeps on turning, so to speak.
I need to find a way to remove the ammonium from the water before I do a water change, and the solution is not an RO filter because that's not in the budget during covid economy. Any ideas on how to accomplish that?