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).