What can i do/clean to lower very high nitrates?

[Reefer Brent]

I agree with removing some of the rear chamber media and rinsing the rest.

I don't think you want too drastic a drop too quickly so that's why I wouldn't remove it all.

To clean the media I would put it in a bucket, with a little tank water, then turn your return pump off. Scrape inside your filter and return sections as much as you can, wipe down your skimmer heater etc, and then suck all of the water change out of the back chambers thus removing as much buildup as possible.

Put your fresh salt water in and test again in 2 or 3 days.

 

[ReneReef]

I don't think you want too drastic a drop too quickly so that's why I wouldn't remove it all.

Not to drastic a drop of what?

If my toilet is blocked and I need to take a dump, I'm not gonna half unblock it first and have half a dump...

 

[MtlReef25]

This all sounds like there is something wrong in the basis.
I would suggest taking measures to increase the overall metabolism of the tank.
That means: increase lighting and flow.

I see four flow pumps. Make them work.
Your corals can take more than you think.

Run high intensity blue and white channels for 6 hours of your schedule.
If your two lights together are ~100W or less. Run them on 100%. You may want to add a third light in this case.

Doing this will make all photosynthetic organisms work harder and take up the nutrients in your tank.
Yes, this includes algae, but with enough herbivores your corals will win. The herbivores will turn those algae into their own mass, detritus for detritivores and skimmable waste.

By the sounds of it, your skimmer might be undersized or running sub-optimally.

Besides this, the sand cleaning advice I would give as well.
And to remove any biological filtration (bioballs, ceramic spheres/blocks etc).
Basically: minimize surfaces in dark oxygen rich areas where nitrification (nitraat making) can take place.


Die?

My previous tank. NO3 at 70. Was over 90 a couple of months earlier. Nothing dead, all growing.

Four months later compared to the previous picture. NO3 still 40. Acros starting to touch the water's surface...

Totally, I've stopped battling with NO3 since the growth is there, everything is fine. NO3 are around 70 and it seems that it is what it is.