I think a stable water parameter is much more important than high nitrate levels. You should break up the huge water change into small ones which can be done more frequently.
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Polypterus Collection Checklist:
Palmas ☑, Polli ☑, Buettikoferi ☑, Ornatipinnis ☑, Delhezi ☑, Senegalus ☑, Retropinnis ☑,
Mokelembembe ☑, Weeksi ☑, Teugelsi ☑, Endlicheri ☑, Congicus ☑, Lapradei ☑, Ansorgii ☑, Bichir bichir ☑.
4'x1.5'x1.5' Planted Tank setup
Amano Shrimp (20) | Neon Tetra (9) | Red Eye Tetra (6) | Glass Catfish (5) | Sterbai Cory (7) | Dwarf Rainbowfish (6) | Black Molly (5) | Kuhli Loach (3) | Dwarf Gourami (4) | Hillstream Loach (4) | Wood Shrimp (2) | Corgo Tetra (3) | Zebra Danio (7) | Dwarf Lobster (5)