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Fish Medication Half Dose

Why half dose with fish medication?

By David A. Lass |

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When medicating tropical fish, there are really only two things that a hobbyist can diagnose and successfully treat – ich and fungus.

Trying to "cure" other supposed diseases by using antibiotics is really foolish, because a) unless you have a microscope and know how to use it you won’t know what the pathogen is, and b) in knocking out the bad bacteria you also knock out the good bacteria of the nitrogen cycle and then pretty much have to start from scratch.

Most problems with tropical fish have to do with water quality, and a couple of partial water changes will usually do the trick.

That said, there is one other thing having to do with medicating fish that really bothers me. Some hobbyists have picked up the idea that on "sensitive" tropical fish they are better off doing half doses of medications. While I know that QuickCure (formalin and malachite green), which is the most widely used cure for ich, cautions to use half doses for scaleless fish like loaches, I have never found this to be necessary. I use QuickCure at full strength whenever I receive shipments of tropical fish, do a water change, or move fish from one aquarium to another. I always use a full strength dosage. Same is true with antibiotics. Using antibiotics (which I do not think is really needed for hobbyists) at half strength also makes no sense to me. It will not achieve the cure that you want, assuming you have stumbled on the right antibiotic. All it will do is to create stronger strains of the bacteria – strains that will become resistant to the antibiotic.

In the commercial ornamental fish industry this is happening at an alarming rate. The ich protozoa has evolved into a new strain of "Super-Ich" that does not respond to QuickCure or copper, the two most commonly used cures. Quinine is the only remedy for the Super-Ich. Treatment of commercially raised tropical fish with the most common antibiotics (tetracycline and triple sulfa) is in certain cases not as effective as it has been, as the bacteria have evolved resistance to the drugs.

In summary, I really do not think that medications, when they need to be used, should be used in anything other than the recommended dosage. The dosage must also be carried out for the specified number of days, even if the tropical fish apparently have overcome the malady. And also, I am really against treating sick fish by raising the temperature and using salt, as it just doesn't make sense to me to stress fish that are already stressed by disease with other stressors such as high temps and salt. This is especially true when we have medications that work well, and do not stress the tropical fish as much.

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Reader Comments

pete    los angeles, CA

9/13/2012 4:19:42 PM

you certainly don't ever use half doses of antibacterial medicines
But, Quick cure or RidIch can be used effectively at a 1/2 to 3/4 dose TWICE a day with sensitive fish or to eliminate hard to get rid of ich infestations. This works better than single doses once a day because it keeps the percentage of medicine higher in the water over the whole day. The medicine dissipates/becomes ineffective in a few hours and redosing keeps up the level.

Kathy    Moose Pass, AK

12/26/2010 9:37:58 AM

A few months ago I had an outbreak of Ick with my recently purchased German Rams. I used the recommended dose of Quick Cure and it worked wonders. The directions stated to use a different amount for tetras that I currenly had in the tank as well but I am glad I ignored this and used the max dose. Rams, tetras and cories all faired well.

ethan    brownsville, TX

6/23/2010 6:35:51 PM

very good article and in fact i would like it if everyone actually did treat their fish with proper dosages of medication. Time after time my customers come in and ask why their medication like tetracycline didnt work and the most logical answer is that they didnt follow through. Like most people taking antibiotics they stop half way throught the treatment because they kinda feel better and dont think twice that they are actually helping the "SUPER" bacteria evolve. Like always kill the weakest and the stronger will survive and thats when things just turn upside down including your fish within two weeks...

sk    nh, CT

6/1/2010 8:10:55 PM


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