Unforeseen situations with your
aquarium can occur at any time, and if you are not prepared to handle a
critical problem when (not if) it arises, losses to your aquarium community
can be costly. You should be ready at any given time to be able to perform
a partial or complete water change, treat a sick fish, or handle any number
of other emergencies.
In some situations, immediate action
may need to be taken and time to waste is something you may not have. For
this reason we feel it is important to keep an emergency first aid kit
on hand, here is a list of basic items we feel an aquarists should have
readily available.
1. Quarantine Tank

Photo by PriceGrabber2. Test Kits

Photo©PriceGrabberBy testing your aquarium water regularly steps can be quickly taken to prevent or head off potential problems. Water tests give you a chemical snapshot of what is going on in your tank water.
3. Baking Soda

Photo by Stan HauterSodium bicarbonate (baking soda) can be used as a quick band-aid to raise the pH in a tank. Found in most kitchens, a dose of baking soda will temporarily suffice in an emergency situation until a water change can be made.
Just dissolve one teaspoon of baking soda for each 20 gallons of tank water in a cup of water, then slowly pour it into your aquarium. The pH change will not be noticeable immediately, so wait for about an hour and test again before adding more. Repeat until you obtain the desired pH level.
4. Ammonia Neutralizer

Photo by PriceGrabberWhen you notice that your fish suddenly have frayed fins and/or cloudy eyes the probable cause is excess ammonia in your tank water. Quickly dosing your tank with a good ammonia neutralizer is the first step to limit the damage. Ammonia neutralizers are also useful in new Quarantine Tanks (QT) until a mature biological filter can be established.
5. Water Conditioners

Photo by PriceGrabberThese products help restore a fish's protective slime coat which is important after an injury has occurred. Many of these products also neutralize ammonia or remove chlorine and chloramines from tap water.
6. Antibacterials/Antibiotics

Photo by PriceGrabberThe most important thing to remember about medications is that many are not reef safe, and some can weaken or completely kill the biological filter in an aquarium, so it is best to treat with any type of medication in a QT, NOT in the main aquarium. Read and follow the directions for recommended dosages and proper protocol closely. Also check to see if they have a shelf life. Since the medications are going to be kept in your first aid kit for emergencies, you want to make sure their effectiveness does not expire.
Treat and prevent the bacterial infections which can follow injuries, pop eye, frayed fins and secondary parasite related injuries.
7. Ich Treatments

Photo by PriceGrabberTreating parasites as soon as they are detected will greatly increase the success of a cure as well as reduce the probability of fatalities. Keep a supply of medications for both Oodinium (Velvet/Rust/Coral Fish Disease) and Cryptocaryon (White Spot Disease). Most aquarists experience both of these parasites at one time or another.

Photo from PriceGrabberRed Slime Algae can pop up from time to time. Red Slime Algae can quickly take over an entire aquarium, choking off the substrate, live rocks and corals. Having an effective treatment on hand when it starts will help you get rid of it quickly.
9. Extra Sea Salts

PriceGrabberHaving an extra week or 2 supply of sea salts held for emergency water changes or setting up a quick QT is always a good idea.
10. Extra Aquarium Heater

PriceGrabberMaintaining a stable water temperature is important for aquarium occupants. Aquarium heaters can and do malfunction without notice. Keeping a spare heater in your emergency kit will help minimize a potential disaster in the future.
11. Activated Carbon
Keeping a couple of pounds of activated carbon in your kit will allow you to quickly filter toxins out of your aquarium water if the need arises.