how often to change the water - Tropical Fish Keeping - Aquarium fish care and resources
 
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post #1 of 6 Old 07-15-2009, 09:23 PM Thread Starter
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how often to change the water

im new to this and ive been reading everything i can get my hands on. once i get my tanks cycled and running how often do i need to change the water and why?
it seems that everthing i read says something different, some say 10% a week some say more or less.

by my logic i would need to change it whenever the nitrates become high. is this right or wrong and why?
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post #2 of 6 Old 07-16-2009, 01:56 AM
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Many things determine the frequency and volume of water that should be replaced. Size of tank,Numbers and types of fish,type of filtration,frequency and types of foods offered. If I were pressed to provide what I felt was suitable recommendation, I would suggest 20 to 25 percent once a week but again considering all variables mentioned,It could be more ,but in my view,, no less.

The most important medication in your fish medicine cabinet is.. Clean water.
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post #3 of 6 Old 07-16-2009, 05:36 AM Thread Starter
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ok im asking about a 90 gal, its got a rena xp3 filter, and it will be stocked with tropical fish fairly heavy.
then i have a 30 gal with a hob filter, stocked with goldfish and catfish, not very heavily.

the 30 gal will eventually be used as a breeding tank for snails and shrimp and im going to get either a 55 gal or a 75 gal for goldfish, channel catfish, and bluegill.
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post #4 of 6 Old 07-16-2009, 05:38 AM
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Ditch the channel catfish. Sooner or later, it will eat your goldfish and bluegill. Besides a 75g is too small for a channel catfish. You are looking for a 180g if you want to house the channel catfish.

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post #5 of 6 Old 07-16-2009, 05:49 AM Thread Starter
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Ditch the channel catfish. Sooner or later, it will eat your goldfish and bluegill. Besides a 75g is too small for a channel catfish. You are looking for a 180g if you want to house the channel catfish.
i would rather have some bullhead just for that reason but i dont know where to get them.
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post #6 of 6 Old 07-16-2009, 08:44 AM
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Quote:
Originally Posted by mattsilkwood View Post
ok im asking about a 90 gal, its got a rena xp3 filter, and it will be stocked with tropical fish fairly heavy.
then i have a 30 gal with a hob filter, stocked with goldfish and catfish, not very heavily.

the 30 gal will eventually be used as a breeding tank for snails and shrimp and im going to get either a 55 gal or a 75 gal for goldfish, channel catfish, and bluegill.
I have a 115g with the same filter, and a 90g and 70g both with an Eheim Pro2. I do a 40-50% partial water change every week, never fail. I agree with 1077, a 25% pwc every week is the absolute minimum. As you, like me, have heavily stocked tanks, more water is better. But less water more often is preferable to more water less often, so get in the habit of doing once a week. Your fish will thank you, and so with the plants if you have any.

The reason for the pwc is biological. Fish produce urine and excrement, and while a filter will remove the solid waste from the water column it cannot remove the liquid which remains in the water until you remove it with a pwc. The solid waste gets trapped in the filter and there it breaks down into liquid. No filter can remove this. The pwc also removes some of the nitrates, which is not so critical in a heavily planted tank because plants require nitrate, as does the anaerobic bacteria in the substrate, but there is still plenty even with a 50% pwc.

An interesting observation: the book that came with my Rena filter suggests a pwc once a month, at which time the filter should be cleaned. Nonsense. In a thickly-planted tank with a smaller fish load, you could manage with no pwc; many aquarists do this. But most of us keep more fish than this regime will accomodate and a pwc of 25% minimum but preferably 30-40% will maintain a much healthier system. Of course, with larger fish more frequent water changes are necessary due to the increase on the bioload from large fish.

Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]
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