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Cycling WITH fish

So, you’ve been told that fish-in cycling is the wave of the future, or you just learned about cycling after having jumped the gun and purchased your tank and fish. Now what? Well, wipe away your tears, dear friend, because there’s hope for you yet!

Fish-in cycling has been used for many years as a viable means to growing beneficial bacteria. In fact, it’s been used ever since Nitrosomonas europaea and Nitrobacter had been discovered and believed to be the natural remedy to toxins in fresh/salt water, as these bacterias oxydize/eat Ammonia and Nitrite – Ammonia, being the waste product of fish and decaying plant/organic matter; Nitrite being the byproduct of oxidized Ammonia. Of course, that theory had been dispelled in 1998 and 2001 by Marine Biologist Dr. Timothy Hovanec, Ph.D. While this process does, indeed, occur, the true culprits, as I’ve mentioned previously, are the Ammonia oxidizing Nitrosomonas marina and Nitrite oxidizing Nitrospira bacterias.

Since fishless cycling had been devised, fish-in cycling has steadily become a thing of the past. Not only is it unnecessary, but it can take much longer to cycle your tank with fish, and it’s also harmful to your fish, thus arguably unethical and can cause early death in the animal inhabitants.

Many local fish stores and big box stores, like Petco or Petsmart, still continue to tell consumers about fish-in cycling, merely because that’s what they had learned as aquarists from years long gone. Fresh in their minds are the days when they were told, as novices, how to use feeder Goldfish or top dwelling fish, like Danios or Mollies, to cycle their tanks. In fact, many of these stores will loan you these “cycle fish.” If any are still alive at the end of the cycle, they tell you that you can bring them back to the store for a refund or in-store credit toward one of your mainstays.

You can’t really fault them for it, because that’s the method they grew up knowing and using… they’re merely passing on their age-old knowledge to up-and-comers like yourself. Of course, you can fault them for not keeping up with the times and knowing their trade. As you’d expect a doctor to keep up on their knowledge of modern treatments, you’d expect an aquarist to keep up on their knowledge of best fish keeping practices. Maybe that’s just wishful thinking. Anyway…

On to the point!

Alright, alright… relax already. As I did for the fishless cycling methods, I’ll lay out the steps needed to fish-in cycle your aquarium via numerical order. We like to keep things simple around here… and by “we” I mean “I.” Onto the goods!

Step 1: Purchase your aquarium, filter, heater, thermometer, substrate, any decorations you’d want (including plants), dechlorinator (ie – Flourish Prime), API’s Freshwater (or Saltwater – depends on your needs) Master Test Kit, and last, but certainly not least, the fish you want to start out with.
– When you’re fish-in cycling, you don’t want to start with too many fish. You’ll want to start with about 3 (depending on the size of your tank). Any more and you’re just asking for trouble.
– When I say “fish,” I don’t mean Neons or Zebra Danios in a 55gal tank. I’m talking maybe 3 Serpae Tetras (or Feeder Goldfish) in a 10-40 gallon tank. Possibly 5-7 in a 40-75 gallon tank. Use your best judgement for 90+ gallons. And since you’ll be doing your best to keep these fish in good health, try choosing fish you want to keep.

Step 2: Rinse your filter out with cold running tap water and fill it with sponge media (which is the mechanical filtration) and bio-media (which is your biological filtration – this is where your BB colony will grow). Your sponge can, however, hold a good amount of BB, as well. This media is all you’ll need. You won’t need anything else, including carbon (which is chemical filtration), ammonia-eating filtration that can be purchased (this defeats the purpose and won’t last forever), or anything else that isn’t a sponge or bio-media.

Step 3: Fill your aquarium with tap water, add dechlorinator, and add your substrate and decor.

Step 4: Raise the temperature of your heater to 82′F. You can keep it at your regular temp for your fish (say 79’F), but raising the temperature will create an optimal environment for growing your BB colony. They enjoy warmer temps and your fish won’t mind the temporary temperature increase.

Step 5: Acclimate your fish to your tank. You can either do this via drip method, bag method, or what I recommend, the plop-n-drop method. The bag method requires you to keep the fish (while in the bag they came in) floating in the tank water for about 10-15 minutes. This is usually acceptable if you purchased your fish from a local fish store, which more than likely has the same quality of water that you do at your home. If your water differs from your fish store, or you mail ordered your fish, then drip acclimate your fish in a bucket for about 1-3 hours. Click here for more information on drip acclimation. Once acclimated to your water’s parameters and temperature, add your fish to the tank.

Step 6: With your Master Test Kit, you’re going to need to test for Ammonia every 24 hours, especially since you’ll be feeding your fish on a daily basis (possibly 2-3 times per day – I would suggest once a day or very small portions 2-3 times a day). Fish waste, including uneaten food will contribute to your Ammonia buildup. Ammonia is obviously the toxin that will harm and can cause death via Ammonia burn.

Step 7: Once you begin to see Ammonia, you need to watch it like a hawk. You want to keep the Ammonia at tolerable levels for the fish, which is <=.25ppm. That means, if you see Ammonia rise to .5ppm or higher, you’ll need to do a water change – it’s normal that the level can surpass .5ppm (be weary of it). Since this will be a daily/bi-daily occurrence, you may need to do daily/bi-daily water changes to keep the Ammonia low. Remember: ALWAYS use dechlorinator when adding new water to your tank. If you’re adding the water from a bucket, add the dechlorinator to the bucket. If via siphon, turn off your filter, add dechlorinator to the tank (enough for the entire tank), and then add your water. Only then should you turn on your filter again.

Step 8: Continue to test for Ammonia on a daily basis, while doing your water changes. If your Ammonia levels seem to be going down a bit (ie – you’re no longer reaching 1ppm or .5ppm every day), start testing for Nitrites. It can take a week or more until you finally see Nitrites building. Be patient. Fish-in cycling takes a lot longer than fishless cycling.

Step 9: Continue to test for Ammonia and Nitrites on a daily basis, while doing your water changes. Nitrites are also a toxic compound and you’ll need to continue doing water changes to keep these at tolerable levels. Tolerable is probably .25-.5ppm, but you’ll always want to aim for 0. So do your water changes to keep your levels down.

Step 10: Once you’ve gotten a reading of 0 Ammonia and 0 Nitrites, you’ll have cycled your tank. This can take several weeks or more. Sometimes it’ll take a couple of months to reach this point. Test your water for Nitrates. If you’ve kept up with your water changes, you should have a reading of about 20ppm Nitrates. It could be lower/higher. You’ll want to do one more water change to get those down to <=10ppm. Finally: It’s about time! After weeks (maybe months) of tumultuous and trying water changes and constant testing, you’ve finally done it! Give thanks to God and bask in the glorious, brightly shining light of victory!

You’ve now grown your beneficial bacteria colony in your biological filter media for the amount of bio-load/stock you currently have. If you should want to add fish later, wait about a week, then add 2-3 more (you could get away with more in larger tanks). You’ll want to add about 3 more fish every other week, so that your beneficial bacteria has time to grow their colony and adapt to the new bio-load.

Once again, if you have any questions, please feel free to ask!

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