Hyposalinity Treatment for Marine Ich: A Step-by-Step Protocol
Hyposalinity (reduced salinity) is a copper-free way to treat marine white spot (Cryptocaryon irritans) in a hospital tank. Learn the target salinity, the ramp rate, treatment duration and why it must never be run in a reef tank with invertebrates.
When to use hyposalinity
Hyposalinity treats marine white spot, or marine ich (Cryptocaryon irritans), a ciliated protozoan parasite, without copper. Because it requires sustained brackish conditions unsuitable for marine invertebrates, it is incompatible with reef systems and must be run in a separate bare hospital tank while the display is left fallow.
Target salinity and ramp rate
UF/IFAS recommends holding at 15 g/L (about 15 ppt) for 21 to 30 days. The Merck Veterinary Manual notes that 16 to 18 g/L is very useful against Cryptocaryon and that constant exposure for at least 3 weeks is generally recommended. Reduce salinity gradually by 5 to 10 g/L per day until the target is reached, then ramp it back up gradually at the end.
Why treatment must run for weeks
The parasite has a resistant encysted stage. The feeding trophont stays on the fish for about 3 to 7 days; the encysted tomont on tank surfaces releases free-swimming theronts anywhere from 3 to 72 days later, most within 4 to 8 days. Only the free-swimming stage is vulnerable, so the treatment must outlast the full cycle — averaging 1 to 2 weeks but ranging up to 11 weeks. Optimal parasite growth is around 23 to 30°C.
Protocol
- Move fish to a bare, cycled hospital tank; leave the reef display fallow.
- Lower salinity gradually, 5 to 10 g/L per day, to 15 g/L (Merck: 16 to 18 g/L).
- Hold for 21 to 30 days — at least 3 weeks, and longer given tomont release up to 72 days.
- Optional combination for stubborn cases: formalin 25 mg/L every other day for 4 weeks, or chloroquine 10 mg/L for 2 to 3 weeks.
- Raise salinity back up gradually and keep monitoring for recurrence.
Sources: ask.ifas.ufl.edu (UF/IFAS FA164); www.merckvetmanual.com ; www.merckvetmanual.com