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If you brought home new fish and suddenly see tiny white dots on their bodies, you are not alone. This is one of the most common problems new and experienced aquarists face. The good news: those white spots are usually treatable, and your fish can make a full recovery if you act fast and follow a plan. This guide explains what those spots are, why new fish often get them, how to tell different causes apart, and exactly how to fix the problem and prevent it next time.
Introduction: Why white spots show up after you buy new fish
Most white spots on newly purchased fish are caused by a parasite commonly called “Ich” or “Ick.” In freshwater, the parasite is Ichthyophthirius multifiliis. In saltwater, the closest equivalent is Cryptocaryon irritans, often called “marine ich.” Both look like grains of salt sprinkled on the fish. Stress from transport, new water conditions, and crowded store tanks weakens fish, allowing these parasites to take hold.
Sometimes white spots are not Ich at all. Fungal growth, bacterial infections, or other parasites can cause spots or patches. Correct identification matters because treatments differ. Do not panic. Take a breath, observe carefully, test your water, and follow the steps in this guide.
Quick look: What you should do right now
First, keep the fish eating and breathing well. Second, test your water for ammonia, nitrite, nitrate, pH, and temperature or salinity. Third, decide if you will treat in a separate quarantine tank or, if you have no inverts or plants, in the main tank. Fourth, choose an appropriate treatment and follow it through the full course, not just until spots disappear. Finally, plan prevention for the future by quarantining new arrivals.
What white spots usually are: Ich explained simply
Freshwater Ich
Freshwater Ich looks like scattered grains of table salt on fins, body, and sometimes gills. Fish often scratch against decor, clamp their fins, breathe faster, or hang near the filter output. Ich has a life cycle with stages that are on the fish, then fall off to reproduce in the substrate, then hatch as free-swimmers looking for a host. Medications only kill the free-swimming stage, which is why you must continue treatment for days after you stop seeing spots.
Marine Ich (saltwater)
Marine Ich looks similar but is not treated the same way as freshwater Ich. Many reef-safe tanks cannot be medicated because copper and other drugs will harm corals, live rock, and invertebrates. In marine systems, you usually remove fish to a separate hospital tank for treatment and leave the display tank fallow (fishless) long enough for the parasite to die out.
Common look-alikes: Not all white spots are Ich
Velvet (freshwater or marine)
Velvet appears more like a fine, dusty coating with a gold, tan, or velvety sheen rather than distinct salt grains. Fish may flash, clamp fins, and show severe breathing issues. Treatments differ slightly and often require light reduction and specific meds like copper for marine velvet (Amyloodinium) or formalin-based treatments for freshwater.
Lymphocystis
This viral condition makes wart-like or cauliflower-looking white to cream bumps, usually on fins. It is not Ich and is not treatable with typical Ich meds. It often resolves with time and excellent water quality.
Fungal growth
White fuzzy patches, like cotton, usually indicate fungus or a secondary bacterial infection, not Ich. These need antifungal or antibacterial treatments and better water quality, not heat and salt.
Flukes and other parasites
Gill or skin flukes may cause irritation, flashing, and excessive mucus that can look like pale patches. A microscope confirms the diagnosis, but many fishkeepers treat empirically with praziquantel for flukes after Ich treatment if symptoms remain.
Why new fish get white spots so easily
Transport and stress
Fish experience stress from netting, bagging, shipping, and unfamiliar water. Stress reduces immune function, giving parasites an opening.
Hidden infections from the store
Fish from wholesalers and stores are often exposed to Ich. You may not see spots at the shop if the parasite is in a stage invisible to the eye. Once home and stressed, the parasite completes its cycle and white spots appear in a day or two.
Uncycled or unstable tanks
Ammonia or nitrite present in new tanks burns gills and skin, lowering defenses. Even a fully cycled tank can cause problems if the filter media was washed in tap water, the bio-load changed suddenly, or temperature and pH swing too quickly.
How to confirm it is Ich: Simple checklist for beginners
Does it look like distinct white grains of salt scattered on the body and fins? Do you see flashing (scratching), clamped fins, and maybe faster breathing? Did the spots multiply over 24–48 hours? If yes, Ich is likely. If the white looks like cotton fluff, large cauliflower clumps, or a dusty golden haze rather than grains, consider a different cause.
Test your water first: Parameters that make or break recovery
Before any medication, test your water. Ammonia and nitrite must be 0 ppm. Nitrate should be as low as you can reasonably manage (ideally under 20–40 ppm). Keep temperature stable. Keep pH steady rather than chasing a perfect number. In saltwater, confirm salinity with a calibrated refractometer (most fish-only tanks around 1.020–1.026 specific gravity). Poor water quality adds stress and reduces the success of treatment.
Setting up a simple quarantine or hospital tank
A basic quarantine works wonders. A bare-bottom tank, 10–20 gallons for small fish, with a heater, small filter or sponge filter, and some inert hiding places like PVC elbows is enough. Use a lid to prevent jumping. Seed the filter sponge from an established tank if possible. During medication, increase aeration because many treatments reduce oxygen in the water. Remove carbon from filters, because carbon will absorb medications. Keep lights low to reduce stress.
How to treat freshwater Ich: Proven methods
Heat and salt method (freshwater only)
Raising temperature speeds the parasite’s life cycle, making treatments more effective. Many aquarists raise freshwater tanks to 30°C (86°F) for about 10–14 days. Add plain aquarium salt, typically 1–3 tablespoons per 5 gallons, dissolved first before adding. Start lower if you have sensitive species and increase slowly. Loaches, Corydoras, some tetras, and other scaleless fish are sensitive to salt and heat; proceed with caution. Do not use this method in planted tanks with delicate plants or with invertebrates.
Pros: Simple and cheap. Cons: Not safe for all fish or plants, and not always sufficient in heavy infections.
Medication options (freshwater)
Malachite green and formalin combinations (such as Ich-X) are classic and effective when used as directed. Follow the product’s schedule exactly and continue for several days after the last spot disappears. Increase aeration during use. Another option is copper-based meds, but freshwater copper use is less common and can be risky for sensitive species. Do not combine multiple medications unless a label specifically says it is safe. Always remove carbon from the filter during treatment.
Duration and what to expect
White spots may disappear after a few days, but do not stop. Continue the full course, usually 10–14 days, to kill the next waves of free-swimmers. Monitor fish behavior; improved appetite and less scratching are good signs. Keep testing water during treatment.
How to treat marine Ich: Safe approaches for saltwater systems
Hospital tank treatment is best
Most effective marine Ich treatments cannot be used in reef displays because they kill invertebrates and can bind to live rock and sand. Move fish to a separate hospital tank. Leave your display tank fishless so the parasite starves out.
Copper treatment (marine)
Use a chelated copper product (for example, Copper Power or Coppersafe) at the manufacturer’s target range, commonly around 2.0–2.5 ppm. You need a reliable copper test kit that matches your copper type (chelated vs ionic). Maintain stable copper levels for at least 14–30 days. Increase aeration, watch appetite, and keep water quality excellent. Do not use copper with invertebrates. Do not run carbon or other resins that remove copper during treatment.
Chloroquine phosphate (marine)
Chloroquine can be very effective but must be dosed precisely. It is usually done in a bare hospital tank. Not all hobbyists can source it legally or safely, and overdosing is dangerous. If you use it, follow veterinary or expert guidance closely.
Hyposalinity (marine fish-only)
Hyposalinity, reducing salinity to around 1.009 specific gravity, can interrupt the parasite’s cycle. This is only for fish-only hospital tanks, not for displays with live rock or inverts. You must lower salinity gradually over 48 hours and monitor with a calibrated refractometer. Raise salinity slowly after treatment.
Fallow period for marine displays
To clear marine Ich from a reef or display tank, run it fishless for at least 6–8 weeks. Many advanced aquarists prefer 8–10 weeks to be safe. During this time, feed the corals as normal and maintain routine maintenance. Without fish hosts, the parasite dies out.
Important safety tips during treatment
Do not overdose
More medication is not better. Overdosing can kill fish faster than the disease. Stick to the label and measure carefully.
Increase oxygen
Most Ich medications and higher temperatures reduce oxygen levels. Add an airstone or raise the filter outlet to ripple the surface.
Remove carbon and chemical media
Carbon will strip medications from the water. Take it out before dosing and keep it out until the course is finished. After treatment, use fresh carbon for a day or two to remove residual meds, then discard the carbon.
Keep filters alive
Do not rinse your filter media under tap water during treatment. If you must clean sponges, swish them in a bucket of tank water to preserve beneficial bacteria.
Cleaning and maintenance while treating Ich
During treatment, do small, regular water changes to keep ammonia and nitrite at zero. Vacuum the substrate lightly to remove cysts that have dropped off the fish, but do not over-clean or disrupt the biological filter. Wipe down glass as usual. Rinse the prefilter sponge in tank water when it clogs. After the treatment course, perform a larger water change and replace chemical media if used.
How long until the fish recover?
With proper treatment, many fish show improvement within a few days, and visible spots usually vanish within a week. Remember that the parasite is still cycling in the tank until all stages are addressed. Finish the full course and observe for another week or two. Appetite should return, breathing should normalize, and the fish should be active and not scratching.
If the spots return: What it means
Recurring spots usually mean one of three things: the treatment was stopped too early, water parameters remain poor and stress persists, or you misidentified the disease and used the wrong treatment. Retest water, consider a different medication, and verify the diagnosis. For marine systems, ensure the copper level was maintained consistently with a proper test kit. For freshwater, consider switching from heat-and-salt to a proven medication or vice versa if the first attempt did not resolve it.
Feeding and supportive care during recovery
Offer small, frequent meals of high-quality foods that are easy to digest. Frozen foods, quality flakes or pellets, and vitamin-soaked options can help. Good nutrition supports the immune system. Remove any uneaten food quickly to protect water quality. Keep lights dim for stressed fish. Add simple hiding places to reduce chasing and bullying. Clean, stable water is as important as the medication itself.
What about plants, shrimp, and snails?
Many Ich medications and salt levels can harm invertebrates and sensitive plants. If your tank has shrimp or snails, or is a heavily planted aquascape, strongly consider treating the fish in a separate hospital tank. Moving sensitive inverts to another cycled tank is another option, but you must then manage the parasite in the original display according to its life cycle.
Myths and mistakes to avoid
“Just raise heat and it will vanish”
Heat alone often is not enough. It speeds up the life cycle, which can help medication timing, but it does not kill every stage by itself. Some fish cannot handle high temperatures long term.
“Garlic cures Ich”
Garlic may stimulate appetite in some cases, which can help fish stay strong, but it is not a cure for parasites. Use proper treatments.
“UV sterilizers will fix this”
UV can reduce the number of free-swimming parasites that pass through the unit, but it will not eliminate an active outbreak on its own. It is helpful as part of prevention, not as a complete cure.
“Stop medication when the spots disappear”
The spots you see are only one stage. Stopping early often leads to a relapse. Finish the full course as directed.
Step-by-step action plan for freshwater Ich
Day 1
Test water and correct any ammonia or nitrite issues immediately with water changes. Decide on treatment: heat-and-salt or a trusted Ich medication. Increase aeration, remove carbon, dose as directed. Dim the lights.
Days 2–4
Maintain temperature, redose medication according to the label, and feed lightly. Watch for improved behavior. Continue testing water daily. Vacuum lightly during water changes.
Days 5–7
Spots should decrease or vanish, but keep treating. Stay consistent and maintain stable temperature. Reduce stress by avoiding sudden changes.
Days 8–14
Complete the full course. When done, run fresh carbon for 24–48 hours if the product recommends it. Perform a moderate water change. Observe fish closely for a week.
Step-by-step action plan for marine Ich
Day 1
Move fish to a hospital tank. Start copper treatment or chloroquine if appropriate and well understood. Increase aeration and keep the tank bare-bottom for easier cleaning. Start the fallow period in the display tank.
Days 2–7
Test copper daily and keep it at therapeutic levels. Feed small meals to maintain strength. Siphon detritus from the bottom. Keep salinity, temperature, and pH stable.
Weeks 2–4
Continue treatment for the full recommended time. Watch for normal breathing and appetite. Do not lower copper early. Keep the display tank fishless for at least 6–8 weeks, ideally 8–10 weeks.
End of treatment
Gradually remove medication per product instructions, perform water changes, and observe for another week. Only after the fallow period ends should you return fish to the display, ideally after they complete quarantine symptom-free.
Prevention: How to avoid white spots next time
Quarantine new fish
Quarantine new fish for 4–6 weeks in a simple separate tank. Watch for signs of parasites and treat if needed before the fish ever see your display tank. This step prevents most outbreaks.
Acclimate slowly and gently
Match temperature and pH as closely as possible. For freshwater, float the bag to equalize temperature and add small amounts of tank water over 15–30 minutes before release. For marine fish, drip acclimation is helpful. Keep lights dim and avoid long netting sessions.
Buy from reputable sources
Choose stores that quarantine and feed fish well. Look for clear eyes, full bellies, good color, and normal swimming. Avoid tanks with dead fish or visible disease.
Keep water quality stable
Cycle your tank fully before adding fish. Test weekly. Do regular water changes. Clean filters properly without killing beneficial bacteria. Avoid sudden changes in temperature, pH, or salinity.
Do not mix equipment between tanks
Use separate nets, buckets, and tools for each tank, or disinfect between uses. Parasites can hitchhike on wet equipment.
Frequently asked beginner questions
Can my fish die from Ich?
Yes, if untreated. Heavy infections can damage gills and skin, leading to suffocation or secondary infections. Timely treatment usually saves them.
Is Ich always present in tanks?
Not always. Many aquarists maintain Ich-free systems through strict quarantine. It often enters with new fish or contaminated water and equipment.
Do I need to treat the whole tank or just the sick fish?
For freshwater displays without inverts or sensitive plants, treating the whole tank is common because free-swimming parasites are in the water and substrate. For marine displays, treat fish in a hospital tank and leave the display fallow.
How do I know when to stop?
Follow the medication’s full course and then observe for at least a week. Do not stop just because you cannot see spots. The parasite may still be cycling.
Special notes for sensitive species
Loaches, Corydoras, and many catfish are sensitive to salt and some medications. Tetras and dwarf gouramis can be delicate when temperatures rise too high. Mormyrids (elephant nose) and scaleless species are sensitive to formalin and copper. Always research your species and start with lower doses when labels advise caution. If unsure, a dedicated hospital tank allows you to control treatment without risking plants or invertebrates.
When to seek expert help
If fish are gasping at the surface, covered in spots, or not improving after several days of proper treatment, ask for help. A local fish store with experienced staff, a fish veterinarian, or a reputable online forum can guide you. Clear photos, water test results, tank size, stock list, and everything you have tried will help others assist you quickly.
Conclusion: Stay calm, act quickly, and finish the plan
White spots on new fish are frustrating, but they are not the end of your aquarium dream. In most cases, you are dealing with Ich, a common and treatable parasite. Confirm the cause, stabilize your water, choose the right treatment, and follow it through the full course. Support your fish with good food and oxygen. For marine tanks, use a hospital tank and respect the fallow period. Then, prevent the next outbreak with quarantine, careful acclimation, and consistent maintenance.
With a clear plan and steady hands, your fish can recover, your tank can stay healthy, and you will become a more confident aquarist. Every challenge teaches you something new. You have got this.