What Aquarium Salt Does — and Does Not Do
Aquarium salt (sodium chloride, NaCl) has several beneficial effects when used correctly in freshwater tanks. It reduces osmotic stress on fish by increasing the electrolyte concentration of the water, making it easier for fish to maintain internal fluid balance. It inhibits the growth of many harmful bacteria and external parasites. And it stimulates the production of the fish's protective slime coat.
What aquarium salt does NOT do: it does not cure internal bacterial infections, internal parasites, or viral diseases. It does not replace proper water quality management. It does not help planted tanks — in fact, it harms most aquatic plants at higher concentrations. And it does not disappear from the tank through biological processes — unlike other treatments, salt only leaves a tank when water is physically removed through water changes.
This last point is critical and frequently misunderstood. If you add aquarium salt to a tank and then top up evaporated water without doing water changes, the salt concentration gradually increases over weeks and months. This "salt creep" can silently rise to levels that harm sensitive fish and kill all aquatic plants.
When to Use Aquarium Salt
Aquarium salt is most useful in these situations: treating mild fin rot (early stage with fraying but no tissue loss), treating external bacterial infections or fungal patches, helping newly purchased fish recover from transport stress, treating ich alongside temperature elevation, and as a preventative addition to goldfish and livebearer (guppy, molly, platy) tanks.
For transport stress recovery: add 1 teaspoon of aquarium salt per 10 liters in the quarantine tank. This reduces osmotic stress and supports the slime coat. Leave for 3-7 days while the fish recovers, then gradually reduce concentration with water changes.
For fin rot treatment: increase to 1 tablespoon per 10 liters (1 gram per liter). Combine with daily 25-30% water changes and improved water quality. Fin rot is almost always caused by poor water quality — treating with salt without fixing the root cause (usually high ammonia or nitrates) will not produce lasting results.
For ich treatment in goldfish or livebearers: use 1 tablespoon per 10 liters combined with temperature increase to 28-30°C. Maintain for the full 10-day treatment cycle. Salt at this concentration combined with heat is effective against ich without chemical medications for these salt-tolerant species.
- ✦Always dissolve salt in a small cup of tank water before adding to the tank — never add salt crystals directly
- ✦Increase salt concentration gradually over 24-48 hours to avoid osmotic shock
- ✦Track how much salt you have added — use a label on the tank or a notebook entry
- ✦Water changes reduce salt concentration — after treatment, gradually remove salt through partial water changes
Correct Dosing: Prevention vs Treatment
Preventative/maintenance dose for goldfish and livebearers: 1 teaspoon per 10 liters (0.5 gram per liter or 0.05% solution). This level is tolerated by most freshwater fish for extended periods and provides mild stress reduction and disease resistance without harming most hardy plants.
Therapeutic dose for fin rot, bacterial infections, or ich (salt-tolerant species only): 1 tablespoon per 10 liters (1 gram per liter, approximately 0.1% solution). This is the treatment level. Maintain for 7-10 days. Do not exceed this concentration for extended tank treatment without veterinary guidance.
Emergency short bath for severely stressed or sick fish: dissolve 1 tablespoon of salt in 1 liter of dechlorinated water at the same temperature as the main tank. Place the fish in this solution for 5-10 minutes only, observing constantly. Remove immediately if the fish shows extreme stress, rolls over, or stops swimming normally. This provides intense osmotic therapy in a short period without the risk of long-term high-salt exposure.
In Cambodia, aquarium salt (muối thủy sản or similar labeled products) is available at aquarium shops in Phnom Penh's Toul Tom Poung market and online suppliers. Use only plain, uniodized sodium chloride — never use iodized table salt or sea salt with additives, which can harm fish.
- ✦Preventative dose: 1 tsp per 10L (0.05%). Treatment dose: 1 tbsp per 10L (0.1%). Never exceed without guidance.
- ✦Uniodized aquarium salt only — iodized table salt and sea salt with additives can poison fish
- ✦Salt baths: maximum 10 minutes, same water temperature, observe fish continuously
- ✦After treatment course ends: remove salt gradually through weekly 25% water changes, not all at once
Fish and Plants That Cannot Tolerate Salt
Never add aquarium salt to tanks containing: scaleless fish (corydoras catfish, loaches, knifefish — they absorb water through their skin and are extremely salt-sensitive), soft-water species (discus, cardinal tetras, altum angelfish — salt disrupts their osmoregulation), or invertebrates (freshwater shrimp like cherry shrimp and amano shrimp are killed by even very low salt concentrations).
Most aquatic plants are damaged by salt at treatment concentrations. Plants showing salt stress wilt, become translucent, and die within days. If you need to treat fish with salt in a planted tank, either remove the plants and treat in a hospital tank, or use a very low preventative dose only — never a full treatment dose.
For tanks with corydoras, shrimp, or sensitive plants, consider alternative treatments for the conditions salt would normally address: for fin rot, focus on water quality and use Indian almond leaves; for ich, use commercial ich treatments (formalin-malachite green based products); for transport stress, use Seachem Stress Guard instead of salt.
- ✦No salt with: corydoras, loaches, shrimp, discus, cardinal tetras, most planted tanks
- ✦Safe with salt: goldfish, guppies, mollies, platies, swordtails, most tetras (short-term)
- ✦When in doubt, use a hospital tank for salt treatment — leave the main tank salt-free
- ✦Indian almond leaves are a safe, plant-friendly alternative to salt for mild disease prevention
Salt in Cambodia's Aquarium Context
In Cambodia's warm climate (26-34°C), bacterial growth is faster and fish are already operating under more physiological stress than fish kept at 22-24°C in temperate countries. This means preventative measures — including judicious salt use for appropriate species — are more important, not less.
Goldfish keepers in Cambodia often see fin rot appear rapidly during the hot season (March-May) when temperatures exceed 30°C and oxygen levels drop. A preventative maintenance dose of salt (0.05%) combined with good filtration and regular water changes significantly reduces fin rot incidence during these months.
At 4848 One Shop, we sell plain aquarium salt by the kilogram and can advise on correct dosing for your specific fish species and tank situation. Contact us on Telegram for personalized advice — we have helped hundreds of Cambodia fish keepers solve salt-related questions.
Step-by-Step Salt Treatment Protocol
Step 1: Identify the problem and confirm salt is appropriate. Is the fish salt-tolerant? Is this a condition salt treats (bacterial, external parasites, stress)? If yes, proceed. If the tank contains shrimp, loaches, or corydoras — use a hospital tank.
Step 2: Calculate the correct dose. Measure your tank volume accurately (length × width × water height in cm ÷ 1000 = liters). Decide on preventative (0.5g/L) or therapeutic (1g/L) dose. Calculate total grams needed.
Step 3: Dissolve salt before adding. Pour the measured salt into a cup of tank water, stir until fully dissolved, then slowly pour into the tank over 30 minutes. Never dump salt crystals directly into the tank — local concentration spikes can burn fish.
Step 4: Monitor and maintain. Check fish behavior for 24 hours. Continue daily water changes if treating a disease. After the treatment period, remove salt gradually through weekly partial water changes — never do a single massive water change to flush salt rapidly.
- ✦Write down: date added, amount added, tank volume, concentration — you will need this for water change calculations
- ✦Never guess tank volume — measure the actual water height, not the tank height
- ✦Salt is cumulative: track every addition and every water change to know your actual concentration
- ✦If salt treatment is not improving the condition within 5 days, reconsider the diagnosis