50ppm is way to high. try to shot for 0. Mine are at <5. What type of water do you use, how aften are water changes. Also I hear about this vodka method along with the suger. I would never but something like that in my tank. Its better to figure out what is causing it and fix it.
I agree, get to the root cause, typically overfeeding, perhaps not using RO/DI, lack of filtration/ skimming.... Looks like you have a large fish population that also demands heavy feedings. This is probably the cause, IMO... The addition of a RDSB or RDSB fuge will help lower nitrates. Your skimmer may also be a bit under-rated to support that very large fish population. Just a guess though. Vodka and sugar dosing can be great, but not to be used unless you really know what you are doing. I like the method personally, but I feed excessively, and dose aminos and coral foods to keep my sps nice and colorful. Again, make sure and start with the skimmer, what volume is it rated for? I would go 2 to 3 times your total water volume if you wish to keep that large of a fish population. Otherwise, you may need to look at another nutrient export method, like mentioned above or a de-nitrator. Good luck!
50ppm isn't likely toxic, nitrate is fairly harmless, many people report nitrates much higher with little issue, so don't panic and do something rash. I've seen some authors suggest 10ppm is ideal, if algae isn't an issue, but hobbyists tend to be overly-paranoid on the issue IMO. The only real problem, at that level will be algae (this can certainly be a big issue). Aggressive skimming, cheato, DSBs etc... will help. The vodka/sugar (carbon source) methods would be a last resort, and personally, I think I might trust a surfer denitrator more (although I didn't say I necessarily trust them - they bring their own issues such as decreased alkalinity).
Skimmers seem to be the best choice IME, if you can upgrade, this would be my first recommendation. GFO will help control algae in the meantime, however won't help nitrates (and could potentially lead to increased nitrates if P becomes limiting). Chaeto tends to be my second choice after skimmers. I'd start there and see what happens. Unfortunately, water changes tend not to help so much with higher nitrate levels, as the levels just rise again shortly after and it becomes tough to keep up (not to say water changes aren't important - the should help keep the nitrates from climbing further at least and may decrease nitrates some if you can keep up).
Thanks guys. I believe my skimmer is plenty adequate. It's rated for up to 250gal. I have a 30 gal sump as well. But, it is probably the third tang (Naso) that tipped it over the edge. Before he came along, nitrates were in the 10ppms. Pooping machines! I fed them seaweed strips everyday for like 2 weeks to make sure that he was eating. And I usually only feed once a day with frozen food-enough for 2 minutes of feeding frenzy. And a strip every couple days. Anyway, I don't have any algae and the corals and fish are doing fine. I was just shocked to see the nitrates that high. I have water changes every week. Anyway, I'll probably cut back the seaweed to twice a week and see if that helps. I might try the chaeto as well. I just didn't know high nitrates could lead to a crash?
Is this the Turboflotor Skimmer? I seriously doubt it's adequate for that fishload regardless at what it's rated at.... typically 2x the rating is required in a reef, for a small fish-load. You have a large fishload and 3-4x the skimmer rating may very well be required.
Nitrates almost certainly will not cause a crash, but Vodka/sugar dosing can... be careful there...