The Dangers of Gross Volume Dosing
When treating sick fish or shrimp, accuracy is the line between life and death. Medications designed for aquariums are formulated based on strict concentration ratios. A common and tragic mistake made by beginners is dosing medication based on the "gross volume" of their aquarium—the dimensions of the empty glass box. In reality, the actual amount of water (the "net volume") in a functioning aquarium is significantly less than its gross volume.
Calculating True Net Volume
To understand why this is critical, let's break down the displacements in a standard 60cm tank (commonly referred to as a 20-gallon or 65-litre tank). The gross volume might be 65 litres. However, an aquascaper typically adds 4 to 6 centimeters of aquasoil to the bottom. Substrate displaces its exact volume in water. Instantly, you have lost 10 to 12 litres of water volume. Next, you add large Seiryu stones, driftwood, and heavily root systems. These hardscape elements further displace another 10-15% of the remaining water.
By the time the tank is filled, a "65-litre" tank may actually only contain 45 litres of actual water. If you follow the instructions on a bottle of medication and dose for 65 litres, you are effectively overdosing the tank by roughly 45%. For robust species, this might cause severe stress. For sensitive nano fish and dwarf shrimp, a 45% overdose of strong medications like malachite green, formaldehyde, or antibiotics is almost instantly fatal, destroying their internal organs and crashing the nitrogen cycle.
Shrimp Sensitivity to Medications
Invertebrates lack the complex hepatic (liver) systems that fish possess to filter out toxins. Dwarf shrimp are exquisitely sensitive to heavy metals, particularly copper. Many fish medications (especially those treating ich or velvet) contain Copper Sulfate as an active ingredient. These are lethal to shrimp at any dose and should never be used in a tank containing invertebrates, regardless of net volume calculations.
When you must treat a shrimp tank—perhaps for bacterial infections or parasites like Planaria and Scutariella japonica—you must use shrimp-safe medications (like fenbendazole or pure praziquantel) and you must dose them with surgical precision using the net volume calculation above. Furthermore, medications often deplete dissolved oxygen in the water. Always increase surface agitation by adding an air stone during any medication protocol.
The Impact on Biological Filtration
Another crucial factor to consider when dosing is the impact on your biological filter. Antibiotics like Seachem Kanaplex do not discriminate; they kill pathogenic bacteria and beneficial nitrifying bacteria alike. An overdose caused by miscalculating water volume will entirely wipe out the beneficial bacteria in your sponge filter and substrate. This leads to a secondary crisis: an ammonia spike. Often, hobbyists believe the disease killed their livestock, when in fact, the disease was cured, but the overdose of medication crashed the cycle, and ammonia poisoning caused the fatalities.
Best Practices for Dosing
- Calculate Twice: Always use the tool above to determine your exact net volume before opening a bottle of medication.
- Pre-mix: Never dump powder or concentrated liquid directly into the tank. Extract a cup of tank water, dissolve the exact dose of medication into it, and then pour the solution slowly into the high-flow area of the filter return.
- Observe: After dosing, monitor the livestock for 30 minutes. If you see erratic swimming, gasping at the surface, or shrimp trying to escape the water, perform an immediate 50% water change and run activated carbon to strip the medication from the water.
- Dilution post-treatment: Once the treatment course is complete, perform a series of calculated water changes (using our Nitrate Dilution Calculator) and add activated carbon to your filter to remove any residual medication.
By treating medication dosing as a precise chemical application rather than a rough estimate, you protect your delicate nano ecosystem from toxic shocks and ensure the rapid recovery of your livestock.