I'm really coming around to the "tanks need phosphates" philosophy, and I've been digging deeper into what the things in my sump actually do. Particularly since my current tank struggles to maintain nutrients in the water column.
I've been discovering that if either nitrates or phosphates hit zero, the other will soon start to rise. Pretty much everything that consumes nitrates and phosphates need to consume both, it's not an either/or situation. If one is missing, the organisms are essentially starving. Kinda like how humans need food AND water to survive. So if your phosphates are low, the organisms in your tank are now phosphate limited and their ability to consume nitrates is reduced. Thus nitrates go up. If your nitrates hit zero, the opposite will happen and phosphates will go up.
And that's the thing about skimmers, they excel at exporting phosphates but really don't touch nitrates at all. They help to export organic waste and particulates BEFORE it becomes nitrates, but don't remove the actual nitrates once they're in the water column. In the example by
@blaxsun, he has that zeovit reactor which acts as a nitrate export element. I've used biopellets in the past, which can be too effective at nitrate reduction.
So you can either reduce your bio-filtration and give the skimmer more time to remove the organics before they convert to nitrates. Or you can reduce your phosphate export by putting your skimmer on a timer. Or you can introduce something that acts as a nitrate export. Every tank needs some experimentation to hit the right balance, and there's no 100% guaranteed answer. A lot also depends on your technical experience and how closely you can monitor complex systems. A common, simple, and mostly self regulating method is a chaeto refugium. But again, you need the phosphates for that to work.
Just, no matter what you do, don't change a lot of things at once trying to chase daily numbers. Most times you hear a horror story about a tank "going wrong", it's usually because there was a sequence of rapid changes to the tank care. Sometimes it's due to equipment failure or other uncontrollable event. But more often than not it's because the owner did a series of drastic things trying to solve a problem, and each attempted solution disrupted the stability of the ecosystem.
