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Medicating fish too frequently


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This is just a general, high-level question, because I am curious . . . . 

At what frequency can one medicate an aquarium?

What I mean by this is, if your community tank displays illness in multiple fish and you run it through a course of meds, and then 6 months later, it incurs some other outbreak, would medicating the entire tank again be detrimental to the fish's health?

I guess I'm wondering how many courses of meds a fish can handle within a given year without this itself becoming a health factor?

Does anyone have experience with this specific case?

I have no sick fish (that I am aware of) currently, so I don't have specifics to give. And, yes, I know one can remove individual fish to a quarantine. And I understand that if fish keep getting sick, check your tank params, etc . . . 

I'm just wondering about meds, and overmedicating by repeat doses spaces far apart, and how that affect fish health short or long term. 

(Imagine you got the sick three individual and distinct times in a year and had to take three courses of medicine as a result . . .  this is what I'm thinking, but about fish.)

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Really good question. I wonder if overdoing antibiotics can have an effect similar to overdoing in mammals, where a resistance of sorts is built up over time against its effectiveness? Another line of inquiry is about treating in tank ca quarantine... could excessive meds pose a threat to overall tank health, not just to fish health? For example, some people treat cyano bacteria (blue-green “algae”) with antibiotics— erythromycin, etc. But at high enough dosage, that can wipe out bacterial colonies and start a chain reaction that compromises balance in the tank as well. 

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5 minutes ago, Fish Folk said:

For example, some people treat cyano bacteria (blue-green “algae”) with antibiotics— erythromycin, etc

Actually, that's an excellent point to bring up. I hadn't thought about that, but i've treated a community tank multiple times in the past two or so years with erythromycin to get rid of cyano, and had not actually thought about that when I originally posed this question as a hypothetical.

So that brings us back to the original thought experiment --  are practices like this detrimental? Or, if there is enough space between episodes of treatment, this is a non-issue?

For me it's not about overmedicating a single dosage, or extending a single treatment period beyond what's recommended. It's just a question of -- over a much longer, extended period of time, what frequency of medication (of a single type of meds or different types) can have an impact on fish health?

And by fish health I'm thinking of direct effects like organ damage, and not indirect effects like impacting biological filters. But I guess those are important considerations as well. 

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I think all of the potential concerns stated so far are valid. I don't think that every 6 months is too much though, especially if it's a different illness.

Using antibiotics always has the potential to make resistant strains if not everything is killed, same as humans/mammals.

Using antibiotics will likely have an affect on beneficial bacteria and heavy overdosing could cause a crash.

Because all of these things are risks though, is why a quarantine tank is recommended. If you are not adding sick fish to the main tank, then it shouldn't have to be treated. If the quarantine tank loses bio mass it's not a huge thing because you can always swap media from your main tank into it.

My other concern would be...if you are medicating often enough to do damage, then what is going on with the tank that you need to medicate so often? Are you not using a quarantine tank and new fish are bringing in disease? I know that things can always slip through, but if you are taking precautions they should be minimal.

If there is one fish in your tank that is constantly getting sick while others show no signs, it could be that it is just a genetically weak specimen. Difficult as it may be, it is often best to cull specimens like that, as you would never want to breed it, and it's going to have a very poor quality of life.

Just some thoughts on the subject....

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