Bessie, here, is demonstrating how to do a freshwater dip.
This is a very effective way to remove external parasites, like ich, flukes, or marine velvet, from the fins, gills, and body of sick fish. Many people also use it prophylactically on new fish. Personally, since I am planning on quarantining new fish in the future, I will avoid the extra stress of a dip unless the fish shows signs of infection. However, for a sick fish, I will not hesitate to dip. Although it does subject the fish to additional stress (not good for an already stressed fish due to illness), the pros outweigh the cons. It can often turn a fish around overnight.
How Does it Work?
Fish are complex, multi-celled organisms. Parasites are not. Fish can withstand low salinity; their bodies are equipped to handle it. In fact, since their cells are actually a specific gravity of 1.015, their bodies have to work pretty hard to prevent water loss and dehydration in a salty environment (e.g. 1.025). (This is one reason saltwater fish are so sensitive to water quality while freshwater fish are not. Saltwater fish are constantly drinking! Freshwater fish are not.) In fact, in a fish-only system, maintaining a lower specific gravity (1.020) can fight parasites and strengthen fish since their cells don’t have to work as hard. Anyway, parasites are simple one-celled organisms and simply don’t have the equipment needed to fight osmosis. When you dip a fish in freshwater, osmosis causes the water on the outside of the cell to flood inwards. Whereas the fish cells have mechanisms to prevent this, parasites do not. The water floods in, the cells swell, and then POP! They burst. No more parasite. Ewww!
Freshwater dips causes parasites to explode!
2. Bowl with lid (to keep fish from jumping out)
3. RO water or decholorinated tap water
4. Heater and thermometer
5. pH meter, baking soda (sodium bicarbonate; raises pH), vinegar (drops pH; shouldn’t need if add baking soda slowly)
6. Airstone or air pump for vigorous aeration
7. Medication (optional; e.g. nitrofurazone (bactericide), antibiotic, methylene blue, formalin, etc.). Read instructions carefully. Many medications are very toxic to fish. For instance, formalin sucks oxygen out of the water and can suffocate your fish. (I learned this the hard way.) Methylene blue is the best since it actually increases the amount of oxygen available to your fish while killing parasites and bacteria simultaneously.
1. Rinse all equipment, nets, and containers to be used with RO water to be sure no traces of contaminants or detergents are present.
2. Mix water. Use RO water or dechlorinated tap water. Heat to 2 degrees above tank temperature (water will cool before use). Match pH (will need to raise pH to make it more basic) by adding little baking soda and stirring. Repeat until desired pH acquired.
3. Add medication (follow instructions carefully).
4. Aerate vigorously with air pump or airstone for 45-60 minutes (longer better).
5. After checking water parameters once more (make sure temperature matches; too hot can actually remove oxygen from the water), you’re ready to start. Remove the fish carefully with a net and put them in the bath for ~5 minutes (I’ve read anywhere from 1 minute to 30 minutes. Less than 2 minutes is probably ineffective. More than 10 minutes may be too stressful.) Continue aeration throughout treatment.
6. Carefully put fish into hospital/quarantine tank.
Use of a few plastic colanders that fit inside bowl used for dip ease stress of fish because less netting is needed.
Medicines are very toxic to inverts and coral. If fish will be housed with inverts, make sure to do a 2nd short dip, or “rinse”, after medicated dip in 2nd bowl (with matching temp and pH).
Dips can be repeated daily, as needed. (Because dips are somewhat stressful, if repeated dips are needed, you may consider treating the sick fish in a hospital tank via hyposalinity and/or daily water changes.