This topic appears from time to time and I just copy and paste what I said previously. You can read the most recent thread about this from 14 August 2019 at the following link.
https://www.fishforums.net/threads/stocking-your-fish-emergency-medicine-cabinet.453684/
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The only thing you should have on hand for fish is salt (sodium chloride) and a dechlorinator. If you are really concerned, then have a bag of Activated Carbon or Highly Activated Carbon, and a bag of Ammogon/ Zeolite (ammonia adsorbing granules) too.
Most fish health issues are caused by poor water quality and a dirty environment. If you do big regular water changes and gravel clean the substrate, and clean the filter, the fish should remain healthy for years. In established aquariums, most diseases occur when new fish are introduced without being quarantined first.
The only reason you should have chemicals sitting around waiting to be used is if you have new fish coming in all the time. Then a number of them will require treatment, but for an established tank, there should be no need for medications.
The first thing to do if your fish get sick is test the water, wipe down the inside of the glass, do a 75% water change, gravel clean the substrate, clean the filter if it hasn't been done in the last 2 weeks, and increase aeration. Then depending on what is going on, you identify the problem and fix it.
The following link has information about what to do if your fish get sick. Some of you have read it and others might not have. Its worth a read when you have some spare time. It's long and boring so print it out and read it in bed to help fall asleep.
https://www.fishforums.net/threads/what-to-do-if-your-fish-gets-sick.450268/
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Having medications sitting around waiting to be used is pointless. It simply encourages people to add chemicals first and hope for the best, instead of finding out what the problem is and what caused it. Then treating the fish if it needs treating.
Medications do go off (expire) and if they are kept in a warm or damp/ humid environment, they break down faster. They can also poison children and animals if not safely stored.
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Anti-biotics should be banned from sale world wide (or at least controlled like they are in some countries), because they cause drug resistance in bacteria that can kill fish, people, animals, birds, reptiles and plants.
If you have bacterial infections appearing in an established aquarium, then you are not looking after the tank (doing water changes, gravel and filter cleaning).
If you look at the fish in the shop, you can see if they appear normal or are sick. If 1 fish looks sick in a tank, don't get any fish out of that tank.
Quarantine ALL new fish for at least 2 (preferably 4) weeks before adding them to the main display tank.