I battled blood red nitrates a while back, because I started my tank with sand and rock from an established FOLWR.
50% water changes weekly for a month, then 25% weekly for a month (with some sand stirring before each change...like 10% of it) , then regular maintenance water changes.
Plus Seachem Prime in the new water to address any ammonia that may come from the sand stirring.
Plus, bacteria dosing with each week with the water changes (I used Seachem Stability) to feed the cycle.
Plus, fresh bio-media that can support the anerobic part of the nitrogen cycle (I used Seachem Pond Matrix in my sump..cheaper than regular matrix and can buy a bucket that supports big bio load for ~$40).
I got my N03 down from ~180 to 0.025 doing this. Probably took between 4 & 6 months...lost track once under 10ppm...haven't seen anything about 2ppm in a long time.
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Good luck!