Large Water Change

[steelhead77]

I'd go for multiple 50% water changes over several weeks. I just did this in my 180 reef with no ill effects. 50% cuts the nitrates in half, another one and now your at 25% of original, another one and now your at 12.5% of original. There will be no shock to the system. No matter what you do, you will NOT have another cycle since cycles are caused from bacteria and stuff dying off and creating ammonia. You're not killing off anything, you're removing poison from the water.

 

[Coasterfrk]

I am presently dealing with the same thing. I inherited a 55g that had nitrates off the chart. The previous owner used tap water high in nitrates and only toped off the tank never did water changes as well as only washed the filters never replaced them. I have been doing water changes at 40% every week and now have them down to 20ppm. The scale stops at 160ppm it took me quite a few weeks to get it to go below 160 so I'm gonna say my tank was easily at 300ppm. My yellow tang was pale and almost white when I got the tank. Now she's finally becoming bright yellow again.