Fish Clindamycin 150mg: Clindamycin for Fish with Fin Rot, Mouth Rot
and Skin Ulcers in Freshwater and Saltwater Tanks
Fish Cin (Fix Cin) is fish clindamycin in 150 mg capsules from Aqua Soma Labs, an antibacterial treatment for ornamental aquarium fish. Each capsule contains 150 mg of clindamycin in a dissolvable powder, and aquarists use it to help manage suspected bacterial problems such as fin and tail rot, mouth rot or cotton-mouth, skin ulcers, and slow-healing lesions in both freshwater and saltwater tanks. The standard aquarium amount is one 150 mg capsule per 10 gallons (38 L) of water, once every 24 hours for 5 to 10 days.
If you used to buy Thomas Labs Fish Cin or Aqua-Cin, Fix Cin is the current replacement and uses the same clindamycin at the same strength. Aquarists reach for it when fish show fin and tail rot, mouth rot or cotton-mouth (often miscalled "mouth fungus"), bacterial dropsy, skin ulcers or lesions, swim bladder problems, or other suspected internal bacterial issues. This bottle provides 100 capsules with fresh expiration dates, enough for larger aquariums or repeat treatment. Hobbyists also search for it simply as fish clindamycin, or by the older Fish Aid clindamycin label.
Use Fix Cin at the first signs of bacterial stress in fish. These are the signs aquarists most often link to bacterial stress:
Important Notice: This product is intended for ornamental aquarium fish only. It is not for animals used for food. Not for human use.
See More +See Less −
Fish Symptoms to Watch For
- Clamped or frayed fins, fin and tail rot
- Reddened areas or red streaking
- Open sores, skin ulcers, or lesions
- Cottony mouth damage or mouth rot (often miscalled "mouth fungus")
- Listlessness or lethargy
- Persistent loss of appetite
Treating early, along with clean water and strong aeration, helps protect the rest of the tank while the affected fish recovers. If your display tank contains shrimp or snails, treat the fish in a separate hospital tank to reduce risk.
Order online and get same-day dispatch on orders placed before 1:30 p.m. CT, Monday through Friday. Ships directly from our U.S. warehouse.
Fish Cin vs Fix Cin: What Changed?
If you previously purchased Thomas Labs Fish Cin or Aqua-Cin, here is what has changed and what remains the same:
Same Clindamycin Formula Fix Cin contains the same Clindamycin Hydrochloride 150 mg per capsule that Fish Cin (Thomas Labs) used. The strength and capsule format have not changed.
New Maker Fix Cin is produced by Aqua Soma Labs, a maker focused on fish and bird treatments. It replaces the discontinued Thomas Labs Fish Cin and Aqua-Cin product lines.
Same Capsule Form The capsule is the same dissolvable powder form that Fish Cin keepers know, so your routine stays the same.
100-Count Bottle Fix Cin comes in a 100-count bottle, a generous supply for larger aquariums, repeat treatment, or multi-tank keepers.
Benefits of Fix Cin for Fish
-
Support for Common Bacterial Aquarium Problems
Fix Cin is often chosen when bacterial problems show up as fin damage, mouth irritation, ulcers, or slow-healing wounds in ornamental fish.
-
Works in Freshwater and Saltwater Tanks
Aquarists use Fix Cin in both freshwater and saltwater hospital tanks, so it fits a range of ornamental aquarium setups.
-
Helpful for External Lesions and Wound-Type Issues
Aquarists often reach for this clindamycin when they see redness, open sores, frayed fins, or recurring skin lesions that may be linked to bacterial stress.
-
Support for Internal Bacterial Concerns
It can be used in a treatment setup when fish show ongoing appetite loss, low activity, or digestive-type signs that can sometimes accompany internal bacterial infections, including deep tissue infections or swim bladder infections.
-
Consistent 150 mg Clindamycin Capsules
Each capsule provides a fixed 150 mg of clindamycin, which makes it easier to plan treatment for both freshwater and saltwater aquariums.
-
100 Capsules for Repeat Treatment and Larger Tanks
The 100-capsule bottle is practical for community tanks, repeat treatment, and keepers who maintain a dedicated quarantine system.
-
Hospital Tank Friendly to Limit Main-Tank Disruption
Treating in a separate hospital tank keeps the treatment where it is needed and lowers stress on the main aquarium. Monitor ammonia and aerate well during any treatment.
Usage Guidelines & Instructions
Directions for Use:
-
Set Up a Separate Treatment Tank
Move affected fish to a hospital tank when possible to make treatment easier and help protect healthy tank mates. If you use chemical filtration (like activated carbon), remove it during treatment, and turn off UV sterilizers if present. Increase aeration in the treatment tank.
-
Dose by Aquarium Water Volume
Add one capsule (150 mg) per 10 gallons (38 L) of aquarium water to be treated. For faster dispersal, many hobbyists pre-mix the capsule contents in a small cup of aquarium water first, then add it to the tank.
-
Repeat Every 24 Hours
Repeat the dose every 24 hours.
-
Perform Partial Water Changes Between Doses
Perform a partial water change between treatments to support water quality. Monitor fish behavior and basic water parameters during treatment.
-
Continue for 5 to 10 Days
Continue treatment for 5 to 10 days, depending on infection severity.
-
Stop if There Is No Improvement by Day 5
If no improvement is seen within 5 days, discontinue use and reassess the likely cause. Consider guidance from an aquatic veterinarian or fish health professional, especially if symptoms worsen.
-
Clear Harmless Yellow Tint After Treatment
To remove harmless yellow discoloration, change 20% of the water and run a charcoal (activated carbon) filter until the water clears.
| Tank volume | Clindamycin per use | 150 mg capsules |
|---|---|---|
| 10 gallons (38 L) | 150 mg | 1 |
| 20 gallons (76 L) | 300 mg | 2 |
| 30 gallons (114 L) | 450 mg | 3 |
| 40 gallons (151 L) | 600 mg | 4 |
| 55 gallons (208 L) | about 825 mg | 5 to 6 |
These figures follow the label-style guideline of one 150 mg capsule per 10 gallons, roughly 15 mg per gallon. Dose by the water volume of your treatment tank, not by the number of fish, give one dose every 24 hours for 5 to 10 days, and round to the nearest practical capsule. The bottle label or your aquatic veterinarian takes priority over this quick-reference chart.
What to Expect During Treatment
Days 1 to 2
Fish may hide or eat less, and the water can take on a harmless yellow tint. This is normal early on. Keep dosing on schedule and keep aeration strong.
Days 3 to 5
Look for signs it is working: sores and red areas stop spreading, fins start to hold, and appetite returns. If there is no change by day 5, or the fish look worse, stop and ask an aquatic veterinarian.
Days 5 to 10
Even as the fish improve, keep treating for the full recommended number of days so the infection does not return. Afterward, change 20% of the water and run activated carbon to clear the yellow tint and any leftover product.
What You Need for Treatment
A little setup before the first dose saves trouble later.
- A separate hospital or quarantine tank, so you are not treating the whole display.
- A heater and an air stone or sponge filter for steady temperature and strong aeration.
- An ammonia and nitrite test kit to track water quality.
- A dechlorinator for the water changes between doses.
- A small net and a clean cup for gentle transfer and mixing the dose.
- Activated carbon to run after treatment to clear the harmless yellow tint.
Pro Tip: Antibacterial treatments can affect biological filtration in some setups, so test ammonia and nitrite and keep aeration high during treatment.
How Fix Cin Works
Fix Cin works by slowing the growth of certain bacteria, which gives the affected fish a chance to recover when treatment is paired with clean water and good care. How well it works depends on the bacteria involved and tank conditions, so it is best used when a bacterial infection is likely and alongside stable water quality.
What's inside: each capsule contains 150 mg of clindamycin as a dissolvable powder. Standard ingredients in the capsule shell hold the powder together and keep it stable in storage. The full ingredient breakdown is not printed on the retail label.
Safety and Tank Notes
When used as directed on the label, Fix Cin (clindamycin) usually causes no problems in ornamental fish. As with any treatment, incorrect amounts, combining multiple treatments, or prolonged use can increase the risk of side effects and resistance.
-
Possible Fish Reactions
Temporary stress or hiding behavior, mild lethargy, and reduced appetite during treatment. Some tanks may show temporary, harmless water discoloration.
-
Stop Treatment and Act Quickly If You Notice
Rapid gill movement, loss of balance, gasping at the surface, rolling over, or fish lying on the bottom. Increase aeration and consider a partial water change.
-
Support Water Quality
Keep aeration high, test ammonia and nitrite, and perform partial water changes as needed between doses.
-
Filtration Notes
Remove activated carbon (and other chemical media) and turn off UV sterilizers during treatment, as they may reduce effectiveness. After treatment, activated carbon can be used to help clear discoloration.
-
Invertebrates
If your display tank contains shrimp, snails, or other invertebrates, consider treating fish in a separate hospital tank when possible.
Important Warnings & Precautions
-
For Aquarium Use Only
Intended for ornamental aquarium fish only.
-
Not for Food Fish
Do not use in animals raised for food.
-
Keep Out of Reach
Store away from children and pets.
-
Storage
Keep capsules in their original container in a cool, dry place at 59-86°F (15-30°C), away from moisture and direct sunlight. Keep the bottle tightly closed.
-
Discontinue if No Improvement
If no improvement is seen after 5 days, stop use and reassess the likely cause. Consider guidance from an aquatic veterinarian or fish health professional if symptoms worsen.
-
Do Not Mix Treatments
Avoid combining Fix Cin with other treatments unless advised by a professional.
Shipping & Returns
Shipping Policy: Orders ship from our U.S. warehouse within 1 business day via USPS or UPS, with same-day dispatch on orders placed before 1:30 p.m. CT (Monday through Friday). For full shipping details, please see our shipping policy.
Refund Policy: If there is an issue with your order, you may be able to return or exchange items within 30 days according to our store guidelines. Before sending anything back, please review our refund policy carefully.
More Fish & Bird Treatments
Fix Mox (Amoxicillin) 250/500mg A treatment for fin rot, dropsy, ulcers, and other suspected bacterial infections in ornamental fish. Available in 30-count and 100-count capsules. Shop Fix Mox
Fix Zole (Metronidazole) 250/500mg A treatment for anaerobic bacterial and protozoal problems including Hexamita and hole-in-the-head in ornamental fish. Available in 60-count bottles. Shop Fix Zole
Fix Doxy (Doxycycline) 100mg A treatment for columnaris, respiratory infections, and Mycoplasma in fish and birds. Available in 30-count and 60-count tablets. Shop Fix Doxy
Fix Zithro (Azithromycin) 250mg A treatment for fin rot, columnaris, gill disease, and avian respiratory concerns in fish and birds. Available in 12-count and 30-count tablets. Shop Fix Zithro
Fix Sulfa (SMZ/TMP) 960mg A treatment for a range of suspected bacterial infections in ornamental fish. Shop Fix Sulfa
Fix Pen (Penicillin) 500mg A treatment for suspected bacterial infections in ornamental fish and non-food pet birds. Shop Fix Pen
Fix Flex (Cephalexin) 250/500mg A treatment for fin rot, ulcers, and bacterial skin infections in ornamental fish and birds. Shop Fix Flex
Fix Flox (Ciprofloxacin) 500mg A treatment for suspected bacterial infections including fin rot, ulcers, columnaris, and septicemia in ornamental fish. Shop Fix Flox
Browse all treatments Explore our complete Fish & Bird Antibacterials Collection for more Fix line products and related treatments.
Guides and treatment tips Visit the Fish & Bird Treatments Blog for practical usage guides, water-care advice and treatment tips.
Frequently Asked Questions
What does clindamycin treat in fish?
In aquarium fish, clindamycin is used for suspected bacterial problems such as fin and tail rot, mouth rot or cotton-mouth, skin ulcers, and slow-healing lesions. It acts against gram-positive and anaerobic bacteria, so it is a poor fit for parasites such as ich or flukes, for true fungal growth, or for viruses. Confirm that water quality is stable before deciding a problem is bacterial.
Is Fix Cin the same as fish clindamycin or Fish Aid clindamycin?
Yes. Fix Cin is the clindamycin fish treatment that hobbyists search for as fish clindamycin, fish treatments clindamycin, or Fish Aid clindamycin. The earlier Thomas Labs Fish Cin and Aqua-Cin used the same clindamycin, 150 mg per capsule. Fix Cin from Aqua Soma Labs is the current version.
What is the difference between Fish Cin, Aqua-Cin and Fix Cin?
Fish Cin was the product name used by Thomas Labs, and Aqua-Cin was another brand of the same capsule. Both have been discontinued. Fix Cin from Aqua Soma Labs is the current direct replacement, with the same clindamycin at 150 mg per capsule in the same capsule form. Only the brand name and the maker changed.
What is inside Fix Cin (Fish Cin)?
Fix Cin contains clindamycin hydrochloride, 150 mg per capsule, supplied as a dissolvable powder inside the capsule. The rest of the capsule is the shell and standard ingredients that hold the powder together and keep it stable in storage. Fix Cin is made and labeled only for ornamental aquarium fish, not for animals raised for food.
What is the fish clindamycin dosage?
The standard fish clindamycin dosage is one 150 mg capsule per 10 gallons (38 L) of tank water, roughly 15 mg per gallon, once every 24 hours for 5 to 10 days, with a partial water change between doses. Dose by the water volume of your treatment tank, not by the number of fish, and scale carefully in tanks under 10 gallons. If there is no improvement after 5 days, stop and reassess the likely cause with an aquatic veterinarian.
Is there a 300 mg fish clindamycin?
No. Fish clindamycin is supplied as 150 mg capsules, and Fix Cin follows that standard, so there is no single 300 mg capsule in this line. The same is true of the 500 mg strength some aquarists look for. Dose by water volume instead of by capsule strength: one 150 mg capsule per 10 gallons (38 L) means a 20 gallon treatment tank takes two capsules and reaches 300 mg that way, and a 30 gallon tank takes three. Measuring the tank is more reliable than splitting or stacking capsules to hit an exact milligram figure.
Is Fix Cin safe for saltwater fish, reef tanks, shrimp and snails?
Fix Cin is used by both freshwater and saltwater keepers, but it belongs in a hospital tank rather than a display. Treatments like this can be hard on invertebrates, so shrimp, snails, crabs and corals should not share water with a dose. Treating separately also protects the biofilter and healthy tank mates, and makes dosing, observation and water-quality control easier.
Can Fix Cin treat fungal, parasitic, or viral problems?
No. Fix Cin targets certain bacterial infections and does not treat parasites, viruses, or true fungal infections. If you see "cottony" growth, confirm the likely cause first since mouth damage is often mislabeled as "mouth fungus."
Where can I buy clindamycin for fish? Do Walmart or PetSmart sell it?
You can order Fix Cin, the current fish clindamycin, directly from Fine Pet Health in 100-count bottles of 150 mg capsules. General retailers such as Walmart, PetSmart, Petco, and Tractor Supply do not carry the Aqua Soma Labs line, so a dedicated online supplier is the reliable route. Orders ship from our U.S. warehouse via USPS or UPS, with same-day dispatch on orders placed before 1:30 p.m. CT, Monday through Friday.
Browse Fish & Bird Treatments Collection →Can I buy fish clindamycin on Amazon?
Fix Cin is sold direct from Fine Pet Health rather than through Amazon. Ordering here means the bottle ships from our U.S. warehouse with a current expiration date and a known count of 100 capsules of 150 mg each. If you do come across fish clindamycin on a marketplace listing, check three things first: the strength should read 150 mg, the count should match what you are paying for, and the expiration date should be visible before checkout, because discontinued Thomas Labs Fish Cin and Aqua-Cin stock still circulates through resellers.