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Tank "accidentally cycling again"???

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Hi All!

I was reading through some guides about cycling a tank, and something this guide said surprised me: http://www.firsttankguide.net/nogoldfish.php

On a note against cycling with goldfish, he says, "Goldfish have different care requirements than do tropical fish, and if you keep the goldfish healthy, and then try to adjust the tank for your tropical fish, you will stress the filter and will cause the tank to at least partially cycle again - you could even cause the tank to completely cycle again."

I've never heard that you can make an already cycled tank cycle again... Or is there something I don't know about (I've only been in the planted tanks hobby for a few months). What instances would cause a tank to go cycling again?

Thanks in advance!

-J
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Cause's of recycle are , improper cleaning of your filter most times
Specifically when someone rinses all of their media out under chlorinated tap water thereby killing most (if not all) of the beneficial bacteria. And/or perhaps when someone has one of those filters that use an all in one cartridge. Throwing out the old and replacing with a new one leaves you with depleted levels of beneficial bacteria (or possibly 0 beneficial bacteria).


But I'm not sure why adjusting tank parameters for keeping goldfish vs tropical fish would affect the cycle at all.
 

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Goldfish thrive in slightly alkaline water, that is roughly room temperature. They tolerate a very wide range of conditions.
Most tropical fish prefer a warmer tank, but there are so many that article should not generalize about water parameters.

Nitrifying bacteria can handle sudden and extreme changes in water parameters, as long as the conditions remain within their range.

How about this:
If you were keeping Golds in their preferred slightly alkaline water (presuming the GH and KH to be perhaps near 10) this would also suggest high oxygen (cooler water holds more oxygen).
Then you switched the tank to very warm (low oxygen) and very soft, acidic water. Nitrifying bacteria need the carbonates, and do not do very much in soft water. Maybe this slowing down is what they are talking about?
 

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Discussion Starter · #5 ·
Thanks! That helps!

Follow-up question! I suspect some bad bacteria, or even small parasites, in my current tank as my betta contracted a mild case of fin rot.

Would cleaning up my media (mostly stones and a small sponge) as you suggested do the trick, or would I have to totally replace the media?

Thanks in advance!

-J
 

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I would start by doing your ordinary cleaning job on the media (simply sloshing it around in used tank water) and a thorough vacuum of the bottom of the tank. Often there are stagnant areas in the tank that tend to trap fallen leaves, and any microorganisms may linger there.

If you do need to sterilize the media then have some replacement bacteria ready. Look for a product with Nitrospira species of bacteria. I just do not see the usefulness of this- whatever is in the media is also in the tank- are you going to take the whole thing down and redo it all? Better simply to clean it well and minimize stress for the fish.
 

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Here is my understanding of why a "second cycle" would happen:

1. During the initial cycle, the bacteria population will have reached an equilibrium point where it is large enough to process all the ammonia the goldfish produces, but there isn't enough ammonia to support the colony growing any larger. The bacteria may still be multiplying, but since there aren't enough nutrients to support a larger population there will be constant die-off, holding the population almost steady.

2. Increasing the temperature will increase the goldfishes metabolism and respiration rate resulting in an increase in ammonia. Now the amount of ammonia exceeds what the bacteria population can process and starts building up in the water column.

3. Now it would be fair to say "a new cycle" happens as the population of ammonia consuming bacteria grows to consume all available ammonia. Since there is a large buildup of ammonia in the water column the bacteria population will grow very large until it consumes the available ammonia and dies back to an equilibrium point with the new amount of ammonia being produced by the fish. The nitrite consuming bacteria population growth and die-off will follow shortly behind the ammonia consuming bacteria

This process actually happens constantly as the fish grow, we just don't notice. Since the bacteria multiply much faster than the fish grow we don't have to wait for the population to grow, there is just less die-off as the bacteria multiply.

We run into trouble in two situations:
1. When the rate of ammonia production exceeds the growth rate of the bacteria colony (e.g. adding fish, faster metabolism/increased feeding, or ammonia pocket released from the soil, etc.)
2. When the bacteria colony population shrinks (e.g. replacing too much media, improper cleaning, etc.)

To be honest, I think we often use the term "cycle" in a way that is rather confusing. I think originally when people talked about the nitrogen cycle they were referring to the constant process by which ammonia --> nitrite --> nitrate.
I think the confusion comes in when we often use the term "cycle" to mean the growth of the bacteria population to an equilibrium point. I know that this confusion of terms initially made it more difficult for me to come to understand the process.
 
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