Medications & Chemical Treatments

When disease strikes, the instinct is to medicate immediately. But every chemical you add to the tank affects the entire ecosystem — not just the sick fish.

How Medications Affect Water

Impact on Beneficial Bacteria

Many medications damage or kill the nitrifying bacteria in your filter:

• Antibiotics (Erythromycin, Kanamycin): Can crash your nitrogen cycle entirely.
• Anti-parasitics (Copper treatments): Less harmful to bacteria but lethal to invertebrates.
• Antifungals (Methylene Blue): Generally safe for bacteria but stains everything blue.

Always monitor Ammonia/Nitrite during and after treatment.

Impact on Plants

• Copper: Toxic to delicate plants at higher doses.
• Salt (NaCl): Most aquatic plants cannot tolerate salt above 1 tsp/gallon.
• Methylene Blue: Blocks light, reducing photosynthesis.

Impact on Invertebrates

• Copper: Lethal to all shrimp and snails at any therapeutic dose.
• Formalin/Malachite Green: Lethal to invertebrates.
• Praziquantel: Generally safe for invertebrates.

Common Water Additives

Dechlorinators (Prime, Safe)

• What they do: Bind Chlorine, Chloramines, and heavy metals.
• Side effect: Also temporarily binds Ammonia/Nitrite into non-toxic forms (for ~48 hours).
• Overdose risk: Very low. Can be dosed up to 5x safely.

Liquid Carbon (Excel, Glutaraldehyde)

• What it does: Provides a bioavailable carbon source for plants. Also kills algae on contact.
• Side effect: Can melt sensitive plants (Vallisneria, mosses). Overdosing kills fish.

pH Buffers

• What they do: Raise or lower pH.
• Side effect: Many are phosphate-based, which can fuel algae growth. Check the ingredients!

Salt (Aquarium Salt / NaCl)

• What it does: Reduces Nitrite toxicity by blocking its absorption. Treats some parasites.
• Side effect: Does NOT evaporate. Only removed by water changes. Harmful to plants and scaleless fish (Loaches, Corydoras) at high doses.

The Hospital Tank

The safest approach is to treat sick fish in a separate hospital/quarantine tank:

• No substrate (easier to clean).
• Sponge Filter only (cheap to replace if bacteria die).
• No plants or invertebrates.
• Medicate freely without risking your main ecosystem.