# Water changes during the cycle



## Grosse Gurke (Jan 3, 2003)

When I first started reading up on the cycle...everyone ways saying to not do any water changes because it would slow down the cycle. Then I talked a little to an old member here DonH...and he said water changes are fine....and actually preferred if you are cycling with the fish you plan to keep...and it can actually speed up the cycle. Well...I wrote up this example in a another thread...but I think it might make a good topic. I am interested to see how people that advise not to do water changes view this example. I am not saying it is proof of anything...it just makes sense to me:

Say you have 5 fish in the tank and each produces 1ppm of waste per day. Thats 5ppm of bio-load your filtration needs to handle in order to have a cycled tank.

So lets make this example a 17 day cycle...bacteria starts the same day...and doubles every 24 hours:

Day 1 through 10 your fish create 50ppm of ammonia and the bacteria consumes zero..end result:
Ammonia = 50ppm, Nitrite = 0ppm, Nitrate = 0ppm
Day 11-12 your fish create 10 ppm ammonia and the bacteria consumes 10ppm ammonia...end result:
Ammonia = 50ppm, Nitrite = 10ppm, Nitrate = 0ppm
Day 13 your fish create 5ppm ammonia..initial bacteria consumes 20ppm ammonia and 5ppm nitrites...end result:
Ammonia=35ppm, Nitrite=25ppm, Nitrate=5ppm
Day 14 your fish create 5ppm ammonia...bacteria consumes 40ppm ammonia and 10ppm nitrites...end result:
Ammonia = 0, Nitrite = 55ppm, Nitrate = 15ppm
Day 15 your fish create 5ppm ammonia...bacteria consumes 5ppm ammonia and 20ppm nitrites...end result:
Ammonia = 0, Nitrite = 40ppm, Nitrate = 35ppm
Day 16 your fish create 5ppm ammonia...bacteria consumes 5ppm ammonia and 40ppm nitrites...end result:
Ammonia = 0, Nitrite = 5ppm, Nitrate = 75ppm
Day 17 your are fully cycled...end result...nitrates at 85 and a 50ppm ammonia spike and a 55ppm nitrite spike....both of which could have been much less by doing small daily water changes. There is never a need to let your ammonia ppm get higher then the bio-load of the tank.

Here is what it would it may have looked like with small daily water changes&#8230;which stop once the bacteria shows up&#8230;and bacteria colonizing at the same rate:

Day 1 through 10 your fish create 50ppm of ammonia and the bacteria consumes zero..end result:
Ammonia = 25ppm, Nitrite = 0, Nitrate = 0
Day 11-12 your fish create 10 ppm ammonia and the bacteria consumes 10ppm ammonia...end result:
Ammonia = 25ppm, Nitrite = 10ppm, Nitrate = 0ppm
Day 13 your fish create 5ppm ammonia..initial bacteria consumes 20ppm ammonia and 5ppm nitrites...end result:
Ammonia=10ppm, Nitrite=25ppm, Nitrate=5ppm
Day 14 your fish create 5ppm ammonia...bacteria consumes 15ppm ammonia and 10ppm nitrites...end result:
Ammonia = 0ppm, Nitrite = 30ppm, Nitrate = 15ppm
Day 15 your fish create 5ppm ammonia...bacteria consumes 5ppm ammonia and 20ppm nitrites...end result:
Ammonia = 0, Nitrite = 15ppm, Nitrate = 35ppm
Day 16 your fish create 5ppm ammonia...bacteria consumes 5ppm ammonia and 20ppm nitrites...end result:
Ammonia = 0, Nitrite = 0ppm, Nitrate = 55ppm

So the end result is an ammonia spike of 25ppm...not 50ppm...and a nitrite spike of 30ppm...not 55ppm. Your tank also cycled in one less day and has enough bacteria to handle your bio-load.


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## Big Den (May 5, 2008)

'Fish in tank cycle' has always necessitated a 10% water change per day, for the sake of the fish, most importantly. I have always preferred fishless cycling myself, easier to control I find.


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## Winkyee (Feb 17, 2003)

When cycling tank, I like to do small daily changes to keep water parameters from getting too far out of wack. It doesn't really mattter if it's an extra couple days to finnish or a couple sooner.


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## Zulu Warrior (Jul 8, 2009)

IMO there is no need to water change during a cycle ... I dont understand why? if you have fish in yes as Den says, but you do it for the fish, not the filter. I had the same thoughts before I got my new shark in my salty! new today so I'm all giddy!

This is a great thread GG, water talk I like!


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## His Majesty (Apr 5, 2005)

as said already, if you got fish in then yes but only for the fish. otherwise waterchange everyday is alot of hassle just for one day less off the whole cycle process.
i always cycle fishless and just let it pan out itself naturally till its ready. no hassle just gotta wate and test.

slight side note, Zulu, what shark you got? any chance you could start a seperate thread regarding it in the salty section? thanks man


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## Ja'eh (Jan 8, 2007)

Nice calculations and info GG.



Big Den said:


> 'Fish in tank cycle' has always necessitated a 10% water change per day, for the sake of the fish, most importantly. I have always preferred fishless cycling myself, easier to control I find.


Agreed! Water changes evryday or every other day with fish for sure but not necessary with a fishless cycle.


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## Piranha_man (Jan 29, 2005)

Amazing GG... you're sounding kinda like Steven Hawking there!


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## Ægir (Jan 21, 2006)

Heres from the other thread i made... the picture kinda helped me to see whats going on.



> For a given bioload there's going to be a roughly set carrying capacity for the bacteria. Whether you do a waterchange or not, you're going to end up at the same place, you just change the path you take to get there and how long it takes.
> 
> If you don't do a WC you finish the initial cycle quicker but you overshoot the carrying capacity, so the population drops, overshooting it again. You end up setting up fluctuations in the population and prolonging the time it takes for the tank to "mature" or finally settle at the carrying capacity.
> 
> ...


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