Treating fish disease requires precision. Overdosing can be toxic to the fish you are trying to save, while underdosing can lead to drug-resistant parasites.
Medications are the #1 reason to use a Net Water Volume calculator. Many medications (like Copper-based treatments) have a very narrow safety margin. Dosing for a 20-gallon tank that only has 16 gallons of actual water can be fatal.
Deciding which treatment will save your fish? Explore our technical comparisons and species-specific treatment guides.
Watching your favorite fish struggle with disease is one of the most stressful parts of being an aquarist. Whether it's the white spots of Ich, the "cotton wool" look of fungal infections, or the clamped fins of internal parasites, the pressure to act fast is intense. However, successful treatment is as much about patience and precision as it is about the medicine itself.
It's tempting to reach for a "broad spectrum" treatment the moment you see a fish acting oddly. But many medications are specialized. Using a parasite treatment for a bacterial infection won't just fail to help—it will stress your fish further and potentially damage your biological filter. Spend the time to properly identify the symptoms before opening a bottle.
If you can, always treat in a separate quarantine tank. This is critical for several reasons:
In the world of aquarium meds, the difference between a cure and a poison is often just a few milliliters. This is particularly true for Copper (used for velvet and Ich) and Formaldehyde (found in many Ich treatments). These chemicals have a narrow "therapeutic window." If you dose for your tank's nominal size (e.g., 20 gallons) but your rocks and substrate mean you only have 15 gallons of water, you are dangerously close to an overdose.
Most medications are oxygen-depleting. When treating a tank, it is vital to increase aeration. Aim your powerheads at the surface or add an air stone. If your fish are gasping at the surface during treatment, it's often not the disease—it's the medicine's effect on the oxygen levels.
Once the treatment course is finished, you need to remove the remaining medication. A large (50%) water change followed by fresh activated carbon in your filter for 48 hours is the standard method to "clear" the water. Don't forget to monitor your ammonia levels closely for a week, as some medications can temporarily stall your nitrogen cycle.
Activated carbon will remove most medications from the water before they can work. Always remove carbon, Purigen, or other chemical media before starting treatment.
Even if the fish look better, many parasites have life cycles that require multiple doses. Always finish the full course as calculated.
Use our precision calculator to find the exact dose for your tank's net volume.
Go to Dosage Calculator
Aquarist, author, and creator of ShrimpKeeper.co.uk. Helping hobbyists achieve professional results through precision dosing.
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