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Before you put any kind of treatment in your pond, aquarium, or treatment bath, you should:


When your fish gets sick, it can be very scary. You might not know where to start, what to do, how to do it, or which product to add to fix the problem. We’ve made a list of 10 rules for when you need to use medical treatments, but you should also check out our Diagnosis Guide and visit your local NT Labs Authorised Retailer for help and advice to make sure your fish get better as quickly and effectively as possible:


  1. Be sure you have a correct diagnosis of the problem.


Before you can treat a disease successfully, you need to know what you are treating. You won’t be able to choose the best treatment for a problem until you know what’s wrong. Changes in the quality of the water lead to a lot of parasite problems. If a disease is thought to be present, the pH, nitrite, and ammonia levels in the water should be checked first to make sure there is nothing else to do before the treatment. Before treating, a partial water change can sometimes help the fish in general.

It is true that many parasitic (or bacterial) infections need the same treatment, and it is often tempting to put a treatment in the pond just to see if it “does the trick.” Even though this may work sometimes, it is not good for your fish or the health of the pond as a whole.

To be sure of your diagnosis, you should (if you can) scrape your skin to look for external parasites and look at them under a microscope to figure out what they are. If you aren’t sure what to do or are worried, go to the nearest NT Labs Authorized Retailer and ask for help.


  1. Remove adsorbent filter material.

Almost all of the medicines fish keepers can use to treat diseases are made from natural substances (even those which claim to contain no chemicals). Adsorbent filter media like carbon and zeolite remove these organic chemicals. Take them out before adding a treatment so that the treatment doesn’t get taken out before it has a chance to work.

As a general rule, the filter mediums can be put back into the filter 7 days after the last dose of treatment has been added. However, you should check the product’s instructions to see if it needs more or less time to work.


  1. Turn off protein skimmers and UV filters.


Ultraviolet (UV) light kills organic chemicals, which is why UV filters are so popular. Because of this impressive ability to sterilize water by breaking down organic chemicals, if it is left on during a course of treatment, the treatment will be destroyed in the same way before it has had a chance to work. Some treatments might even become dangerous when UV light hits them. It is a good idea to turn off the UV during treatment. To give the treatment the best chance of working, you should also leave UV filters off for at least 7 days (the longer, the better, up to 10 days if you can).

Like active filter media (see point 2 above), protein skimmers can take out a treatment’s active ingredient before it has had a chance to work. To stop this, turn off the protein skimmer for at least two hours after you take your medicine. But be careful. Remember that skimmers are an important part of a marine aquarium’s aeration system for keeping high levels of dissolved oxygen for your fish, corals, and other invertebrates. If you turn off the skimmer for a long time, make sure to turn up the air flow to make up for it and keep the level of dissolved oxygen in the aquarium stable.


  1. Let in more air.

Many treatments for diseases can lower oxygen levels, but none of them will be hurt by adding more air, so it is best to do that if you can, especially if you are treating a pond when it is warm outside. You should also keep in mind that the amount of oxygen in ponds may be lower in the morning because the plants that make oxygen underwater use oxygen at night when there is no light. Because of this, fountains and other things that bring in air should always be running 24 hours a day during a course of treatment.

Unless they have a lot of plants, oxygen levels will change less in aquariums than in ponds. No matter what size or shape the aquarium is, though, it is best to add more air while treating it.

If the water gets cloudy after a medicine has been added, it could be because you’ve taken steps to make sure the treatment has the best chance of helping your fish. As these bacteria that cause cloudy water grow, they will use up the oxygen in the water, leaving less oxygen for your fish. Make sure to give your fish as much oxygen as possible as soon as you add the treatment.


  1. Don’t treat fish unless you have a lot of time to watch them.

After a diagnosis has been made and confirmed, it is important to treat sick fish as soon as possible. But keep in mind the time of day (because it affects the amount of dissolved oxygen) and how long you have to watch the fish after adding the treatment. Don’t put the treatment in your pond or aquarium and then go to work or bed, just in case your fish have a bad reaction to the treatment. Even if you’ve used the treatment many times before, the fish could still have a bad reaction this time. If that happens, you’ll need to be there to change the water, add more air, or do whatever else is needed to stop the reaction. Over time, the water conditions in aquariums can get worse, so adding treatments may change the chemistry of the water one time but not another (nitrate concentrations may be higher, GH and KH levels may be low, the pH level may be higher or lower, etc).

If you’re not sure how the water is or why a disease needs to be treated, you can always test the water with one of our multiple-test kits (such as Pond Lab Multi-Test Kit or Aquarium Lab Multi-Test). It’s possible that the infection took hold because the water quality was getting worse, so you should check the water quality regularly and before adding any medicine. Before adding any medicine, it’s a good idea to do a partial water change. This will help refresh and improve the environment for your fish. As with all indoor water changes, be careful not to add water that is a very different temperature from the water in the aquarium. Doing so could cause both healthy and sick fish to become even more stressed.


  1. Don’t mix medicines together.

The only thing that doesn’t follow this rule is anything that only has malachite green or formaldehyde in it. Malachite and Formaldehyde from NT Labs’ Koi Care line can be used together, but for your convenience, we’ve made a product that already mixes them in the right amount. For more information, see our FMG Mixture.

We don’t recommend mixing any medicines (other than the ones listed above), especially if they are made by different companies. We will only be able to give you our “best guess” as to how your fish may react. Neither you nor any of the manufacturers will know how the effects of the mixtures may add up, be unpredictable, or be dangerous. It is much better to only use one manufacturer’s products at a time because they will be able to give you the best advice on the problem. But you shouldn’t mix them together!

During our time at NT Labs, we’ve heard a lot of common myths that aren’t backed up by science. One of these is to never use formaldehyde in water that has salt in it. The only unproven explanation we have heard for this is that formaldehyde will come out of the water as a gas if salt is present. We don’t think this is likely because formaldehyde is used in marine aquariums, where the salt level is much higher and it works fine. When there is salt in the water, there is no scientific reason not to use formaldehyde.


  1. If you don’t feel better after 7 days, you should try a different medicine.

Give the treatment time to work and break down on its own, and change some of the water, before adding another treatment that might react with the first. If the problem doesn’t get better after the first treatment, check the diagnosis and make sure you added the right amount and that the treatment is the best one.

Malachite green and formaldehyde, for example, are not good ways to treat skin and gill flukes, fish lice, or fin-rot. Even though they might help by getting rid of any skin parasites that could be making the problem worse, the main symptoms will still be there and your koi pond will need treatments like Flukasol, Permanganate Dip, and Acriflavin.

When you look at a scrape of skin under a microscope, you might see both parasites and flukes. If this is the case, you will need to decide which problem is worse (in this case, the flukes or the parasites) and treat that problem first. If a skin scrape shows a lot of different parasites, you may just need to change the water. This is because a lot of different diseases is a sign of bad water quality, unless you have added new fish without quarantining them first. When you have both a parasitic and a bacterial infection, it is usually best to treat the parasites first. When these external parasites die, they often leave small open wounds where they have penetrated the skin. These wounds can get infected again. This will cut down on the number of courses of antibiotics that need to be taken, but if the bacterial problem is the most urgent, treat it first.


  1. Watch out for the water temperature.

When it is cold, parasites, bacteria, and fish all have slower metabolisms. This is why fish eat less in the winter (coupled with the fact that they are generally much less active in the winter than in the warmer months.) In the same way, medicine will work slower in colder water, so it may take a little longer than usual for the treatment to work and you may need more than one course of treatment.

Because of these things, it can be hard to decide whether or not to use treatments in the winter. We have a responsibility to take care of our fish, so we suggest that you fix any problems in your pond now. If you don’t treat the parasite or bacteria, they may spread (slowly) and get a stronger hold, making it harder to treat when the water temperature does rise.

Even though it is safe to use Koi Care Formaldehyde at temperatures below 10°C, please store it and any other products that contain formaldehyde above this temperature.


  1. Feeding

As long as the fish are still eating, it is usually okay to feed them while they are being treated. But always follow the feeding instructions on the treatment’s label, and don’t be tempted to give too much food. If the fish are very sick and don’t seem to be eating much anyway, it would be best to stop feeding them for a few days at the start of treatment until they get their appetite back. This will keep the water quality from going down. In general, NT Labs’ food doesn’t react with treatments or change how filters work, so fish can be fed while treatments are going on in the pond or aquarium. Please remember that food that isn’t eaten will go bad and may pollute the water, which will lower the quality of the water. If fish aren’t interested, don’t feed them.

If, on the other hand, the biological filtration system is damaged by adding a treatment that isn’t used right or a medicine that hurts filter bacteria (all NT Labs products are safe for filters at their working concentration), feeding the fish could cause the levels of nitrite and ammonia to rise, which would lower the water quality and make the fish feel stressed. Check the water often during treatment and for the rest of its life. Routine testing of the water will show you how your pond’s natural cycles work and can help you find and fix a problem before it hurts your fish. Keeping an eye on your water while you are treating it will also let you know if the treatment has hurt the filter bacteria. If so, you can choose the right filter bacteria product to help the filter get better.


  1. Do what it says on the label of the bottle.

This could be the most important rule. The Veterinary Medicines Regulations say that the dosage rate and instructions must be written on the label of every animal medicine. Always follow these directions, measure the dose carefully, and don’t be tempted to add a little extra for good luck.

If you follow these rules, you should be able to treat your fish without any trouble. However, as the saying goes, “prevention is better than cure.” By testing for ammonia, nitrite, nitrate, pH, KH, and GH in your water on a regular basis, you can spot problems that are often caused by bad water quality. Sometimes all it takes to stop a disease or infection from spreading is to change the water, and regular testing can save you a lot of time and trouble in the long run.

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