Hyposalinity Treatment Marine Protocol Guide
Hyposalinity is the quieter third option alongside copper and TTM — a medication-free treatment that kills marine ich by exploiting the parasite’s inability to osmoregulate at reduced salinity. A hyposalinity treatment marine protocol is the choice for copper-sensitive species that cannot tolerate Cupramine and for keepers who prefer a non-pharmaceutical approach. This guide from Gensou Aquascaping at 5 Everton Park covers the precise salinity ramp, the duration, and the species-specific notes that make the difference between a successful treatment and a stressed dead fish.
How Hyposalinity Works
Marine Cryptocaryon parasites cannot survive at salinities below 1.009 specific gravity (equivalent to roughly 14 ppt). Most marine fish, by contrast, can osmoregulate down to that level without acute harm provided the change is gradual. Drop the salinity to 1.009, hold for four weeks, and the parasite dies out while the fish stabilises. It is elegant in theory and delicate in execution; the ramp rates and the hold duration both matter.
What It Does Not Treat
Hyposalinity does not reliably kill marine velvet (Amyloodinium), flukes, or bacterial infections. Assume hyposalinity covers ich only. For velvet-suspect fish, copper or chloroquine is required. For flukes, praziquantel. For bacterial secondary infections, a concurrent antibiotic dosed according to label. See marine velvet treatment for the velvet pathway — hyposalinity is the wrong tool there.
Setup Requirements
You need a calibrated refractometer (not a plastic hydrometer — accuracy matters at this salinity), a dedicated hospital tank with no live rock or substrate, fresh RO or RO/DI water for dilution, and a reliable heater and flow. The hospital tank needs a cycled sponge filter. Bare tanks or plastic bins are preferable to anything porous or copper-contaminated. Total setup in Singapore runs $200 to $400 depending on whether you already own a refractometer. Our refractometer calibration guide covers the zeroing and maintenance of this critical instrument.
The Salinity Ramp Down
Never drop salinity suddenly. Start at the fish’s current salinity (usually 1.025) and reduce by 0.002 SG per day over roughly eight days, reaching 1.009 on day eight or nine. Remove about 10 percent of the tank water daily and replace with pure RO until the target is reached. Temperature, pH and oxygen must stay steady during the ramp — stressed fish handle osmotic changes less well. Test salinity each evening before you change water the next morning. Overshooting to 1.008 or below can kill fish as surely as the parasite.
The Hold Period
Maintain 1.009 SG for four full weeks, then begin the ramp back up. During the hold, do small water changes using pre-mixed 1.009 SG saltwater to maintain ammonia and nitrite at zero. Adjust ramp-back at 0.002 SG per day, returning to 1.025 over roughly eight days. Total protocol is around six weeks from start to finish — slightly longer than copper. Skipping the last week because “the fish looks fine” is the most common failure; parasite tomonts hatching late in the cycle need the full window to die out.
Species Tolerance Notes
Most bony marine fish handle hyposalinity well — tangs, clownfish, wrasses, angelfish (smaller species), damsels, basslets and gobies all tolerate 1.009 adequately. Sharks, rays, and seahorses do not and need alternative protocols. Invertebrates cannot be treated this way at all; hyposalinity is strictly for fish, in a dedicated hospital tank. Fish species with unusual osmoregulation or compromised health going in are candidates for copper or TTM rather than hyposalinity.
Monitoring During Treatment
Check salinity twice daily during ramps and once daily during hold. Test ammonia and nitrite daily — a stressed biofilter at low salinity is less efficient, and ammonia creep is common in the first week. pH usually drops slightly in hyposaline water; target 8.0 to 8.2 with small buffer additions if required. Watch fish respiration — elevated gill movement that does not settle within 48 hours indicates a ramp that is too fast or an underlying issue not addressed by hyposalinity.
Feeding During Hyposalinity
Fish appetite usually holds through the ramp if it is gradual. Feed normally during treatment, using soaked pellet to help hydration. Skipping feeding is unnecessary and counterproductive during the four-week hold — the fish needs the nutrients to rebuild any parasite damage. Rinse leftover food out within ten minutes; the lower salinity and reduced biological filter capacity mean rotting food matters more than in a normal tank.
Combined Protocols
Hyposalinity pairs well with secondary treatments. A single prazi dose early in the protocol handles flukes that are resistant to hyposalinity alone. A short antibiotic course during week two addresses bacterial secondary infections. Do not combine with copper — the two do not stack effectively and copper still carries its own species-tolerance issues. Our freshwater dip protocol covers short-duration alternatives for fluke and other external parasites if a concurrent dip is warranted.
Return to Normal Salinity
The ramp back up matters almost as much as the ramp down. Raise salinity by 0.002 SG per day by pre-mixing 1.025 saltwater and substituting it into the tank slowly. Watch for any returning parasite signs during and immediately after the ramp up, and into the subsequent two-week observation period. A well-executed hyposalinity rarely relapses, but the observation window catches the rare ones.
When Hyposalinity Is the Right Choice
Hyposalinity is the sensible first pick for copper-sensitive species — mandarins, anthias, some wrasses — where the treatment target is ich alone and velvet risk is low. It is also the choice for keepers who are philosophically uncomfortable with copper or who have had bad experiences with over-dosing. For keepers new to marine quarantine, copper is still the more forgiving default because the margin for error in salinity measurement is smaller than the margin for error in copper testing.
Note that hyposalinity is a hospital-tank protocol; never run it on a reef display because corals, live rock and invertebrates will die at 1.009 SG. Always pair hyposalinity treatment of fish with an appropriate fallow of the display if the display has been exposed to ich. The copper-safe fallow reef guide covers the display side of the protocol.
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