It's all about balance. You need good enough flow, a good enough skimmer, good enough maintenance practices, and the right critters in the tank to help by pecking at rocks (keeping detritus from settling). Phosphate is troublesome with algae, you want that to stay low.

Saying that, I know two tanks personally that are way overstocked and way, way, way overfed (think 4x what they need). One of those tanks sits around 40-60 ppm nitrate (a few softies) and the other is close to 100 ppm (it's fish only, no skimmer). Neither tank would sustain SPS corals, but there isn't a speck of algae in either tank and both tanks have reef lighting.

It's true.I know a friend who have sps only tank and he keeps the phosphates and nitrates to zero with bio-pelets and on the same kind of sps mine looks better then his
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People keep their tanks wiyh nitrates for the corals to feed but you have to keep phosphates low but I wouldnt go over 10 for nitrates. I have tried this approach and it works but you have constant algae and detritus build up. Always cleaning your glass, changing filter socks, vacuuming sandbed, etc and im not a big fan of more maintenace. Now I keep nitrates and phosphates at 0, but I add a few drops of amino acid and the somtimes sps food. A lot less work for me, better colours and growth. All, i do now for maintenace is empty the skimmer cup and wipe a very light dust off the glass every 7-10 days. Let your equipment do the dirty work for you in your tank!

I would say that it depends heavily on the corals themselves. Some are perfectly fine with a "dirty" tank while others won't stand for it at all. In this regard it is a bit of trial and error. I've run my tank with 5ppm nitrates as well as near zero as well as above 10. I've had SPS survive all 3 levels of nitrates but I've also had SPS die at all 3 levels. Over last summer my skimmer died and my bioPellets ran out so I was running a fairly dirty tank. I had a lot of SPS that were fine, but I also had a few completely brown out and some even died. When I turned the tank around (new skimmer, new pellets), all my browned out corals regained their colour. All my dead corps remained dead. I'm probably running somewhere near 1-3ppm nitrates and near zero (but not exactly zero) phosphates at the moment. I've found my best results to be 1-5 ppm nitrates.

Kien how u keep it constantly at that lvl of nitrates? Just test daily and feed more/less? Do u run Gfo n have macro algae? How many hours do u run blues/white lights?

Well, for me it's mostly based on experience. I don't actually try to keep it at that level. It just happens to fall at that level due to my setup. So, it's not constantly at that level. Or at least I don't think it is.

I've been running bioPellets for the past 5 years, and I know that (for me) the bioPellets don't reduce my nitrates down to absolute zero. I've tested this with a pinpoint nitrate meter and at best they drop down to maybe 1ppm or somewhere near there. My nitrates will read "zero" on standard chemical test kits (API, etc), but I know that it's not really zero. It's more like "almost zero but not quite, probably 1ppm or lower". Again, verified with a pinpoint nitrate probe. If I take my bioPellets off line and just rely on skimming my nitrates will go up and hover around 5. That's just what it does with good skimming and water changes.

I control phosphates with GFO in a media bag and just let it do its thing. With GFO running my phosphates typically drop down to near zero as well. That is, zero as read on standard phosphate test kids (API, hana, etc). But again, I know that this doesn't mean that my phosphates are at absolute zero.

In addition, I think I feed fairly heavily and have a fairly heavy bioload.

My Blue lights (22K T5s) for 12 hours (10am to 10pm) while my halides (14K) run for 6 hours.