Cycling a 120, how long? - The Planted Tank Forum
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post #1 of 6 (permalink) Old 07-14-2010, 10:27 AM Thread Starter
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Question Cycling a 120, how long?

Hi all,

Just wondering how long I should cycle my 120 gallon tank for?

It's been going for a week. I used eco-complete as a substrate which said it helps to cycle tanks quickly. There are no plants or fish in it yet. I tested the water today and got the following results:
Nitrate - 0ppm
Nitrite - 0ppm
Ammonia - 0ppm

I have a CO2 system, just waiting for the cylinder which I will pick up towards the end of the week and start dosing to bring my pH down. its currently at 7.8. Is this how I should adjust the pH or should I use another means?

So I guess I have 2 questions, 1) what are my test readings telling me (this is my first foray into a planted tank) and 2) when can I start planting

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post #2 of 6 (permalink) Old 07-14-2010, 11:16 AM
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1) You have no source of ammonia in your tank, therefore all your readings will be 0. Get some liquid ammonia and dose until you get 5ppm. If you cant get liquid ammonia, adding fish flakes or raw shrimp will give it some ammonia as well. You will see ammonia rise, then drop while nitrites rise, then nitrites will drop and nitrates will start rising.

2)You can plant whenever, plants are not affected by those levels of ammonia
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post #3 of 6 (permalink) Old 07-14-2010, 01:20 PM
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I agree with Penguin. Sounds like you need to do a bit more research on cycling the tank. There is no specific length of time that you cycle it for - you cycle it until the cycle is complete - usually 4-8 weeks. The *basic* principal is that fish produce ammonia, which is a deadly toxin. There are bacteria that convert the ammonia into nitrite, which is also deadly. Luckily, there are bacteria that convert the nitrite into a much less harmful chemical called nitrate. When you cycle the tank you are basically growing these bacteria in the tank so that when you add fish they will do their job of converting the ammonia into nitrite and then into nitrate. In order to start this process you need to add a source of ammonia to the tank so the bacteria you are trying to grow have a food source, and you will need to continue to add ammonia until the cycle is done. Typically once the cycle starts you will get ammonia readings, then eventually you'll start getting nitrite readings and the ammonia will start to go down, then eventually you'll see nitrate readings. When the cycle is finally complete your test readings will show 0 ammonia, 0 nitrites, and readable nitrates.

Do a search on "fishless cycle" and you'll find lots of information.
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post #4 of 6 (permalink) Old 07-14-2010, 01:59 PM
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I agree with everything said except you can plant right now! Stuff as many plants as you can in now.

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post #5 of 6 (permalink) Old 07-14-2010, 02:42 PM
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add a bunch of plants and.... some fish. It's a 120. The fish won't be affected to any great extent by the amount of ammonia they'll produce in a tank that big. Just add slow and let the tank cycle as you go. The plants will suck up the rest.

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post #6 of 6 (permalink) Old 07-14-2010, 02:48 PM
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Do NOT use raw shrimp. Read here:

There are other methods of fishless cycling being recommended or used however one method being pushed on the internet is the use of Raw Shrimp; however this is a recycled idea (which included the use of silversides, frozen shrimp, and even dead feeder fish) and has reappeared on the internet even though it was debunked in the early 1990s.

I do not recommend this method, not because it does not work for cycling, but because it may also allow a Saprolegnia infection to get started in your new aquarium. Saprolegnia is a mold (often called a fungus) that easily gets a foot hold in decaying nitrogenous matter such as raw shrimp and I have seen this many times in my experiments. Even after the source of Saprolegnia growth is removed, the secondary zoospores which are the primary mode of pathogenic transmission can remain, even after large water changes/vacuumings.
A new tank is the worst time to have a Saprolegnia infection get started as this is when fish are often much less resistant to disease due to the stressor of a new tank environment.

Another note/point is that even the fish food method (as noted earlier) can allow for Saprolegnia to get a foothold in an aquarium if food is simply dumped into an aquarium, making this method not any better than the “Raw Shrimp or Silversides” method as its decay will also attract Saprolegnia, so make sure to liquefy fish food prior to addition to your aquarium when used for cycling.



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