Naturally Occurring Chemicals in Fish Tanks

This page is the CodyCross answer for the clue below from Tundra and Taiga, Group 1687, Puzzle 2 (Burrowing Petrels).

Question is: Naturally Occurring Chemicals in Fish Tanks

and the answer is: NITRITES

Word Meaning:

NITRITES — plural of nitrite

Definitions from Wiktionary.