What is the best way to finish up a fishless cycle?

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steph101

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Jan 7, 2014
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Finally I am done. Its been 4 looonnnng weeks!

Ammonia- 0ppm
Nitrite- 0ppm
Nitrate- 40-80ppm
18 gal

How do I finish up? I plan on getting fish within 24 hours from now.
 
Okay, thanks.
What happens if I do the pwc and the nitrates don't go down?
 
If your nitrates are potentially 80, you should do more than 50%. You want to get them under 20. I would recommend at least an 80% water change. If they don't go down, you will have to do another one until they do. But I don't know why they wouldn't.
 
If your nitrates are potentially 80, you should do more than 50%. You want to get them under 20. I would recommend at least an 80% water change. If they don't go down, you will have to do another one until they do. But I don't know why they wouldn't.

Last time I did a 80 per cent change and nitrates stayed the same, not sure as to why. I will give it another go though and see what happens..

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Was it in a cycling tank or one with fish? I know nitrates can spike in tanks with fish if you stir up the substrate a lot because waste gets mixed into the water column.
 
In a cycling tank

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When the tank is cycled I would do the biggest water change you can 12-24 hours before getting your new fish. Just suck out every last bit you can and fill it with new water (with proper dechlorinator of course) and do not re dose the ammonia.
 
Last time I did a 80 per cent change and nitrates stayed the same, not sure as to why. I will give it another go though and see what happens..

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Is it possible that you were maxed out on the test kit the first time. In other words you may have been well above the maximum level and the water change just brought it down but still above max level so they remained the same colour?

I would also check your tap water for ammonia nitrite and nitrate.
 
When the tank is cycled I would do the biggest water change you can 12-24 hours before getting your new fish. Just suck out every last bit you can and fill it with new water (with proper dechlorinator of course) and do not re dose the ammonia.

I usually dose in the morning and I wont have time to do water change till tonight so should I dose ammonia in the morning before I do the water change?

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Do not do a near-100% water change, you will de-stabilise the conditions you have maintained to develop a good colony of bacteria. Just begin adding fish...... they will provide the ammonia for the bacteria and your tank will continue to cycle... it is a never ending...er...cycle!
 
I apologize, I don't agree with that...
The tank was fishless cycled and it needs the water change before adding fish. The nitrates are really high after a fishless cycle and the water change is the last step in preparation. We always recommend a very large water change at the end of the fishless cycle before adding fish. I don't see how this will destabilize anything at all.
 
I apologize, I don't agree with that...
The tank was fishless cycled and it needs the water change before adding fish. The nitrates are really high after a fishless cycle and the water change is the last step in preparation. We always recommend a very large water change at the end of the fishless cycle before adding fish. I don't see how this will destabilize anything at all.

+1
You don't want to add any new fish into a tank that has just finished fishless cycling without a huge water change because nitrates are going to be through the roof..
Almost all the bacteria lives in the filter so it should stay perfectly stable.
 
I apologize, I don't agree with that...
The tank was fishless cycled and it needs the water change before adding fish. The nitrates are really high after a fishless cycle and the water change is the last step in preparation. We always recommend a very large water change at the end of the fishless cycle before adding fish. I don't see how this will destabilize anything at all.

No apologies please - people disagree with me all the time :)

Beneficial bacteria need stable conditions too, so in my opinion a huge water change may be detrimental as the new water is unlikely to be of exactly the same chemical balance as that taken out, so could shock the bacteria and slow down or halt their matbolic processes. Then fish are added and produce ammonia which is not broken down sufficiently, resulting in possible problems for new fish. I have read a few threads now on here and other forums, where people have still had.problems with ammonia in a fishless cycled tank, just after adding their first fish.
 
I've always understood that you want to do the largest water change possible at the end of fishless cycle. One of the benefits to fishless cycling is that your biofilter is built like a freight train.

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