Medication dosing
Calculate the right dose for common aquarium medications, with species warnings based on your stocking.
Manual overrides
By default the calculator reads your saved stocking roster (if you've used the stocking calc) to surface species-specific cautions. If you don't have a saved roster, or want to ignore it for this calculation, toggle the override here.
What this does
Pick a medication, enter your tank volume, and the calculator gives you the dose for that volume along with re-dose schedule, water-change schedule, and carbon-removal advice.
Liquids come out in millilitres. Products sold as packets (API General Cure, API E.M. Erythromycin, Fritz Maracyn) come out as a packet count, and the tub products come out in scoops or measures, because none of those labels say what a packet or a scoop weighs. When a quarter-packet figure is more than a few percent off the real number, the exact amount is shown next to it. Salt comes out in rounded spoons, the way API's label gives it.
Every dose, schedule and caution here is taken from the maker's own label or product page, and where a label says nothing about something (scaleless fish, shrimp), the calculator says so rather than guessing. Read the label on your bottle anyway. Formulations change.
If you've used the stocking calculator on this site, your roster is saved. The medication calc reads that roster and surfaces specific cautions for what's in your tank. Treating fin rot with KanaPlex and you have shrimp? The shrimp warning is highlighted, not buried.
What's in the database
- PraziPro (Hikari): flukes, tapeworms, internal parasites. 5 ml per 20 US gallons, one dose left in for 5 to 7 days. Hikari lists no compatibility issues in freshwater, shrimp included.
- API General Cure: internal parasites, hole-in-the-head, flukes. Two versions with different doses: packets (1 per 10 US gallons) and the scoop tub (1 scoop per 20 US gallons). Two doses 48 hours apart either way.
- Ich-X (Hikari): ich. 5 ml per 10 US gallons every 24 hours, until 3 days past the last spot. Hikari says it can be used with shrimp and snails if you watch them; shrimp keepers often report losses anyway.
- ParaGuard (Seachem): ich, velvet, flukes, fungus, fin rot. 5 ml per 40 L daily. Seachem says to remove invertebrates and to start scaleless fish at a quarter to half dose.
- KanaPlex (Seachem): bacterial and fungal infections, fin rot, dropsy. One measure per 20 L every 48 hours, three doses at most. Seachem says to remove all invertebrates before dosing the water.
- API E.M. Erythromycin: gram-positive bacterial infections. One packet per 10 US gallons, four doses with a water change in the middle.
- Maracyn (Fritz): erythromycin for columnaris, fin rot, popeye, gill disease. One packet per 10 US gallons daily for 5 days, water change on day 6. Fritz lists snails and other invertebrates as compatible.
- Aquarium salt (API): 1 rounded tablespoon per 5 US gallons. Only the general-use dose; the stronger salt treatments people use for some diseases aren't on the label and aren't calculated here.
What the cautions mean
Scaleless fish are species without conventional scales: catfish (cories, plecos, otocinclus), loaches (kuhli, clown, hillstream, weather, yoyo), eels, and similar. They tend to be more sensitive to medication. Seachem's ParaGuard label is the only one here with a reduced starting dose for them; for the others the label is silent, and the calculator tells you that.
Shrimp and snails are where labels disagree most. Seachem says to take invertebrates out before ParaGuard or KanaPlex goes in. Hikari says Ich-X can be used with them under close watch, and Fritz lists them as compatible with Maracyn. Crabs and crayfish in your roster get the shrimp caution too. When in doubt, a hospital tank for the fish is the safe option.
Biofilter suppression matters for antibiotics. Fritz says Maracyn may inhibit nitrifying bacteria; Seachem says KanaPlex doesn't harm the filter bed. Test ammonia and nitrite daily during any antibiotic course anyway.
Why remove carbon
Activated carbon absorbs organic molecules, including most medications. If you dose into a tank with carbon running, the carbon removes the medication faster than the fish can absorb it, neutralising the treatment. Pull the carbon before dosing and put fresh carbon back after the course. Some labels also want UV sterilizers, protein skimmers or Purigen out of the loop; the Filter line in the results says which.
Why re-dose
Most parasites and bacteria have life cycles where some life stages are immune to the medication. Praziquantel kills adult flukes but not the eggs, which is why PraziPro allows a retreatment after 3 days or more. Ich treatments need to continue through the free-swimming theront stage, which only emerges from cysts under the substrate, so the treatment runs longer than the visible spots persist.
Stopping treatment when fish look better is the most common reason treatments fail. Run the full course.
When to call a vet
The calculator handles standard dosing. It doesn't handle: dropsy, advanced bacterial septicemia, suspected mycobacterium, parasites that don't respond to standard treatment, anything with neurological symptoms. If your fish has a problem you can't identify confidently, a fish vet (yes, they exist; search for an aquatic vet near you or ask your local exotics vet) is worth more than experimenting with medications.
Related tools
- Stocking - Load your roster for species-specific warnings.