Cloudy Water after Dosing Fish Tank with Antibiotics

We have all been there: a desperate hobbyist with sick fish who are in need of some real meds. Sure, you may have tried rounds of salt or epsom salt baths, herbal remedies, clean water, etc., but that doesn’t always cut it. When you have found yourself in a situation where your aquarium isn’t getting any better, and your fish aren’t getting any healthier, it’s time to go for the hard stuff. But sometimes, even after you dedicated yourself to following medication directions to the letter, we wind up with new problems we didn’t have before.

If you followed the directions on the label of whatever antibiotic you chose, and trust me there are plenty, you probably used an envelope of powder, waited 24 hours and performed a water change. After a few days on repeat, you do a large water change and add charcoal filters to soak up the leftovers and neutralize everything again. A night or day later, however, you may notice cloudy water in your fish tank and feel you’ve done something wrong. Never fear, though, this is part of the process of utilizing antibiotics.

First you need to have an idea of what antibiotics are before you can understand what happened to your tank. The word antibiotic simply means “against life”, which is pretty self-explanatory. Whenever you use antibiotics, they quickly go to work eradicating all bacteria in sight, good and bad. All life forms are supported by bacteria, and aquariums are no exception – beneficial bacteria keep your fish in check! These different types of beneficial bacteria live in your filter media, substrate, as well as any other porous surface (like driftwood, or faux decor), working hastily to break down fish waste. When beneficial bacteria is disturbed, either met with new competition or killed completely, you end up with cloudy water (much like the water throughout a new cycling). This can happen with something silly, like adding new plants that are covered in their own beneficial bacteria.

Basically, the antibiotics sufficiently finish off your cycle, and send you back to square one. Do not pass Go, do not collect $200. Now, you have a few options when it comes to starting things up once more, and we will talk through them here. First off, you can seriously consider doing a fish in cycle, where you cycle a tank while it houses fish. I would never suggest starting a new tank this way, especially if you’re a beginner, but in the case of a cycle crash we don’t always have a choice. Fish in cycles require larger weekly water changes, if not daily water changes, to remove waste depending on your stocking levels. You won’t have to add ammonia with this method of cycling, simply because the inhabitants are doing it for you with their own forms of ammonia. Be sure to research fish in cycling further online before proceeding.

There’s a better way, though, for those of us who keep multiple tanks running on their own, individual, closed systems. Although it requires a bit more electricity and effort to maintain water quality, it is a good setup when you need to sneak some bacteria over to a sick tank. If you can spare a filter sponge, take one out of a healthy tank and replace it with a new one. This works by adding bacteria back into the uncycled tank, although it’s not the same as the previously established colony that tank once housed. Alternatively, you can also take a sponge from a healthy tank and wring it out over the media of your sick tank, or into a bucket to then add to your other filter. There is some small risk involved, as water from the affected tank could infect your healthy tank. And if it reaches your other tanks, either by use of shared hoses, or various equipment, like sharing sponges, your entire stock is prone to end up sick once more, considering antibiotics lower the immune system – it’ll just become a vicious cycle.

Quarantine tanks can be invaluable to any fish keeper, especially in regards to singling out sick fish or saving the cycle of any given tank. If it’s an illness that won’t spread, or your fish are suffering from injury prone to infection, setup a separate tank for healing time or rounds of treatment. This can save the cycle of your regular tank, and prevent the need to suffer through cycling again (which can last anywhere from 2 to 4 weeks). Whichever method you choose will work, just with a few different requirements to get you there.

Do not fall trap to purchasing bottled bacteria, or bacteria in a bag (usually sold as substrate). This kind of bacteria is usually short lived, with an unknown shelf life. Consider how your tank must be maintained with water agitation and a thermometer to keep it’s inhabitants alive and thriving, before considering buying a bag or bottle of water. Take it at face value, move on, and learn how to cultivate your own strain of beneficial bacteria. Your tank will be happier for it, and you’ll gain important knowledge and experience moving forward.

To wrap things up, make sure to cross your t’s and dot your i’s before purchasing any kind of antibiotic treatment – one brand and type is not the same as another. The package’s details can further explain how it will effect your beneficial bacteria, as most antibiotics are prone to do. More than likely, it will wipe out all bacterial life forms within the tank, which is to be expected.

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