Free fish disease tool
Hyposalinity treatment for ich means slowly lowering a fish-only hospital tank to 1.008–1.010 SG (about 11–13 ppt) and holding it there for at least 30 days, a salinity marine ich can't survive but most fish tolerate. This planner works out how much water to swap with RO/DI at each step, then builds a dated calendar for the drop, the hold, the slow raise, and the display tank's 76-day fallow, with copper and tank transfer schedules too.
Hospital tank
Actual water, not the tank's label size.
Raise back at up to 0.001 SG per day.
28–42 days; 30 is typical.
The day fish leave the display (day 0).
Confirm it's ich before you start. Velvet moves much faster than ich and needs treatment the same day; hyposalinity is not a reliable cure for velvet or brook.
| Disease | What you see | How fast | Usual treatment |
|---|---|---|---|
| Marine ich (Cryptocaryon irritans) | Distinct white grains like salt on fins and body; flashing (scratching on rocks); spots come and go in cycles. | Days to weeks | Hyposalinity, copper, or tank transfer in a hospital tank; leave the display fallow 76 days. |
| Marine velvet (Amyloodinium ocellatum) | Fine gold or gray dust that looks like powdered sugar; rapid breathing; fish hang at the surface or near flow. | Can kill in 1–3 days | Emergency: freshwater dip plus copper or chloroquine right away. Hyposalinity does not reliably work. |
| Brooklynella (clownfish disease) | Thick, peeling mucus or slime patches, pale skin, heavy breathing; most common on clownfish. | Can kill in 1–2 days | Formalin bath and treatment; copper and hyposalinity are not effective. |
Salinity above 1.000 comes from dissolved salt, so the planner works on the excess (SG − 1). Replacing a share of the tank with RO/DI keeps the rest of the salt, so the share to swap is 1 − (new − 1) ÷ (old − 1). Going from 1.025 to 1.009 in one go would swap 64% of the water; the planner splits that into two or three daily steps. The raise uses the same balance with saltwater mixed a little stronger than normal.
Ich spends most of its life as cysts on rock and sand, where no treatment reaches. Treating only the fish works if the display has no fish to reinfect for long enough that every cyst hatches and the free-swimming stage starves. Corals, snails, and shrimp can stay; ich can't live on them.
Step 1
Set up a bare-bottom quarantine tank, move every fish out of the display, and note the date. The display stays fishless for 76 days.
Step 2
Pick hyposalinity, copper, or the tank transfer method, then enter the tank volume, salinity, temperature, and start date.
Step 3
Make each water change, dose, or transfer on the dates shown and test salinity, copper, ammonia, and pH as listed.
Step 4
Raise salinity or remove copper, observe the fish, and acclimate them back once the display's fallow date has passed.
Marine ich (Cryptocaryon irritans) can't complete its life cycle at a salinity of 1.009 SG (about 12 ppt) or lower. Most keepers hold 1.008 to 1.010 SG, measured with a refractometer calibrated in 35 ppt fluid. At 1.011 or higher, some ich strains survive.
Hold fish at 1.009 SG for at least 30 days after reaching the target, and 28 to 42 days depending on how cautious you want to be. Then raise salinity slowly, no more than 0.001 to 0.002 SG per day, before returning fish to the display.
No. Corals, snails, shrimp, starfish, and other invertebrates die at hyposalinity levels, and live rock bacteria are harmed too. Move fish to a bare-bottom hospital tank and treat them there while the reef display stays fishless.
Both work when done correctly. Hyposalinity is gentler on most fish and uses no medication, but needs a precise refractometer and takes about a month at target. Copper works in 14 or more days and also treats velvet, but some fish tolerate it poorly and it needs daily testing.
Leave the display tank without any fish for 76 days. That covers the longest time ich cysts have been recorded surviving and hatching without a host, so the parasite starves. Corals and invertebrates can stay in the tank.
Size and set up the hospital tank you'll treat in.
Drip fish back into the display once treatment and fallow are done.
Mix the saltwater you need for water changes and the slow salinity raise.
Plan the extra water changes that keep quarantine water clean.
Measure how much water is really in your quarantine tank.
Check pH, ammonia, and other readings against safe ranges.
Keep the hospital tank at a steady 77–80 °F.
Treating freshwater ich instead? Work out aquarium salt doses.