I never had a problem keeping Nitrates low. If your biological filtration and mechanical is good then you should not really have an issue keeping low. If you have big fish that eat alot, it will be much higher 10-20PPM+, which is great bc coral love nitrates. You can easily control Nitrates by increasing tank circulation, sump turnover,, adding more biological media (rock or other), wet skimming. But all else fails then you can always remove some fish. Take a good look at the fish food your feeding and how much nutrients are going in vs out. Also, use a good nitrate test kit like salifert, if you can get it.
My issue is lowering Phosphates, it goes from 0.10 to 0.60 in as little as 1 week. My nitrates stay stable at 10PPM in the same time. I bring it down by dosing lanthanum chloride. Something I want to avoid doing long term since its not really helping my nutrients stability since I test it every 1-2 weeks and it last week it was at 0.60 and I can bring it down to .010 in 48 hours but these swings can't be good. I also never used GFO and want a sustainable solution so going to build a algae turf scrubber.
If I was in India or any other place where supplies are limited, I would 100% build a Algae turf scrubber. These will remove PO and NO and other bad metals in your water and much cheaper than buying GFO and maybe even good enough to work without a skimmer.
