Help please!!

Glad to hear you seem to have things under control, but I would like to add to the thread for future readers with a similar problem. First, abruptly dropping the nitrate levels, especially that high, will seriously stress and even kill tank inhabitants. Since nitrates are at the end of the ammonia cycle they build up slowly, and since they aren't nearly as harmful as ammonia and nitrites, they can get very high without adverse affect. Your critters can adjust to this if it happens slow enough, although it will shorten their life span and weaken immune systems.

Because frequent water changes can lower nitrates quickly, depending on the source, they can cause more harm than good. The best way to take care of super high nitrate levels is slow and steady. Algae and bacterial species that break down nitrates are best. If you have the cash/know how to set up a refugium, awesome. If not, you gotta add bacteria.

Had this issue with my old freshwater tank and hunted down an additive that I can only describe as bottled stink. "Microbe-lift Special Blend" First time I used it my wife cleaned our Savannah Monitor's house, scooped the litter boxes, searched the house for dog mines, and finally asked me if I was having digestive issues. I'd say don't smell it but, well, then you would. It's added in small doses over a few weeks, which sucks since you have to build up some nerve before opening the bottle after the first time.

My freshwater tank leveled out after about a month and had less frequent ammonia/nitrate spikes. Oh, and my f/w red snook would dance in the cloud each time I poured in another dose of filth. No other effects though.

Used the same treatment in our new (about three months old) reef tank to help with ammonia spikes after feeding. Same result, but caused brown algae breakouts 24hrs after. Nothing our dollabella couldn't handle though. Also saw major growth in purple, white, green, and pink bacterial colonies on our live rock after second dose. Stopped after three doses and tank seems happy now.

Skepticism is a must in the aquarium world with all the snake oil additives, but for this issue I gotta say this horrible brown liquid passed the test.

 

My SO is a big guy, I have to use a big brush to paint him with LOL.

 

aww, come on now, would'nt be more fun with "finger paints"
...that's what I'm talk'n'bout. LOL 8)