an exhaustive explanation to Water Change Theory

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shekes

Jessica Rabbit
MFK Member
Aug 14, 2005
626
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Toon Town
There are sooo many threads on WCs and I always encounter the same mistake:
People believe that 2 small WCs are the same as one big one as long as they change the same amount of water. It is wrong.
If you do 2 WCs, when doing the second one, part of the water you pump/suck/siphon out is the "clean" water you put in in the first waterchange.

Now here is formula I copied without permission:
"The waste in the tank on the evening (after a WC) of the first day = W(1-WC%)

Waste in the tank after second day (after WC) = W(1-WC%) + W(1-WC%)(1-WC%)

Waste on third evening = W(1-WC%) + W(1-WC%)(1-WC%) + W(1-WC%)(1-WC%)(1-WC%)

Etc., etc.


In English it means the fish are constantly putting out waste and it is being partially removed every evening with the water change, so the waste builds up over time. It is shaped like a learning curve where it is steep at first then gradually levels out to a nearly constant amount (the time to level out (flattening of the curve) varies with the WC% but is around one week for most of our situations). The actual curve if done by hours would actually form a sawtooth pattern but still in the general form of a learning curve."

For a more exact info click here

If you have difficulty understanding, you can do the following experiment:

Take a bottle of milk and perform small WCs on it. Try pouring out some 5% as some "small WC followers" suggest and refill with water. Shake and repeat. Shake and repeat. Shake and repeat. Shake and repeat. Shake and repeat. Shake and repeat. Shake and repeat. Shake and repeat. Shake and repeat. Shake and repeat. :wall:

You'll see that it will take you a whole damn day to get the water in the bottle absolutely clear. If you pour all the milk out at once and refill with water it will take a few seconds.

Of course a 100% WC is not an option for most fish and people.

Therefore the decision on how big and often you WCs should be, is a trade off between a big one that stresses the fish and a small one than stresses the fish-keeper.

Not thaaaaat complicated really.
 
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CentralMayhem

MONSTER FISH EATER
MFK Member
Mar 30, 2005
826
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San Diego, California
rock on Shekes. thanks for the explanation bro. we appreciate your contributions. One thing though. I HATE MATH. hahahah. good thing you worded it for the average MFK'er. keep the info comin
 
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repair

Feeder Fish
MFK Member
Jul 12, 2005
2,156
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Indy
It is an intersting post.

I don't know that I agree that doing large water changes stress the fish but I will agree that anytime you can have less wast build up in a tank it is healthier for the fish. :thumbsup:
 
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xoticaddiction

Jack Dempsey
MFK Member
Dec 19, 2005
20
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angus, Ontario, Canada
yes but long interevals between water changes to do one big one vs multiple water changes mroe frequently is healthier to the fish imo

u have to think about why we are doing water changes
a:) to remove nitrates
b:) to remove solid waste or detrittus if u prefer

so lets say instead of a 25% change every week we do 50 % change every two weeks thats 2 weeks of nitrates building into higher more toxic levels by allowing that waste to stay there

now i am not going to pretend that i know the numbers at all i am a mere hobbyiest not an expert by any means

but lets pretend i have a clue if it was to take one week for ure nitrate levels to raise to 10ppm with your fish load lets assume that in 2 weeks it will be 20ppm which is highly unlike because as time passes in that two weeks more and more waste is coming so u may end up with a number that is 25-30 ppm

it makes since to me that it would be best to use frequent small water changes in order to keep detrituss from building up and in essence slowing and inhibiting the level of nitrates and the bimonthly poisoning of ure fish

i currently am involved in saltwater and have been for quite some time but prior to that i was a piranha keeper and i used the frequent small water change theory and people were amazed by the color of my reds. Yhere are some really good filtration methods in saltwater that i am interested in setting up a new freshwater pred tank jsut to see if these methods are able to cross into the freshwater world, and if they were there would be no need for for either frequent or large water changes it would be as simple as a consistent siphoning of detrituss thru a filter of some type and staying on top of evaporation as well as the ocassionall water change once a month type thing

keep in mind everything i said above is based on personal theories would love to see some real world testing results to support either method
 
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rallysman

Polypterus
MFK Member
Aug 7, 2005
17,533
32
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indiana
repair said:
It is an intersting post.

I don't know that I agree that doing large water changes stress the fish but I will agree that anytime you can have less wast build up in a tank it is healthier for the fish. :thumbsup:
Click to expand...
Maybe you should also mention that you do water changes literally 24X7X365 in some of your tanks :thumbsup: :thumbsup:
 
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ChickenTeeth

Feeder Fish
MFK Member
Nov 30, 2005
299
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Canada
In my view , gravel cleaning is not essential in planted tanks. I believe we often keep our tanks too pristine. Water quality is important, but a little mulm on the bottom of the tank is no bad thing. The organic waste matter has various functions - the extra dissolved organic carbon generated by plants and fish reduces toxins from heavy metals, and enables plants to absorb nutrients. Also certain fish need bacteria in their gut and, if the tank is too clean, these will not be availiable to help digestion!
:WHOA: :WHOA: :WHOA:
 
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