Dosage of organic carbon (vodka/vinegar)
Dosed vinegar or vodka to feed denitrifying bacteria and reduce nitrates without water changes.
Detailed explanation
Organic carbon fuels heterotrophic bacteria that consume nitrates and phosphates. Start with 0.1 ml for 100 litres/day and gradually increase.
Biopellets are the safest alternative. The risk of overdose is a potentially lethal oxygen crash.