# Water Change Calculator



## MOA (Jan 7, 2010)

hello,

This is a follow-up to my concejtures about water changes in general. I have made a spreadsheet that allows users to test several water-change scenarios based on their current data. Also, it allows users with contaminated water sources to see how beneficial/nonbeneficial particular water change schedules are. Moreover, this spreadsheet was inspired by TheAquaTools.com and is meant to be a general tool as well. Unlike many of my recent spreadsheets, it is an Excel 97-03 file and thus should be read by most programs.

Water Change Calculator by MOA (MOA's: How Many Fish?, Stocking Freshwater Aquariums)


Please tell me what ya think,

MOA


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## MOA (Jan 7, 2010)

Nothing? No comments at all? I didn't think it was that boring .

Oh Well,
MOA


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## WhiteGloveAquatics (Sep 3, 2009)

Its a good read, I saved the site and will be using it from time to time.

around here, a response is far and few between unless your thread is deemed argueable then you get all the responses you dont want, mainly from the staff.


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## MOA (Jan 7, 2010)

Hello,

I have made several updates to my website. Of those changes is the addition of a form that allows users to submit fish species for future Fishsheets. So I was wondering--what fish should be added?

HMF Home (MOA's: How Many Fish?, Stocking Freshwater Aquariums)

MOA

P.S. You can either respond to this thread or one the online form on the website.


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## beaslbob (May 29, 2009)

MOA said:


> Nothing? No comments at all? I didn't think it was that boring .
> 
> Oh Well,
> MOA


gee i missed this somehow.

Anyway after years and years of not doing water changes and many many discussions on how water changes prevent buildups, replace trace elements and so on, I spend 3.5 micro seconds studying how come my tanks work with no water changes.

I first asked myself--- self: why do my tanks work? 

Self answered back. Hey dummy what happens if you have something in the replacement water that is increasing or decreasing in hte tank at some constant rate? How much of that thing do you have just before each water change when that value is not increasing or decreasing?

So I spend another 3.5 micro seconds and came up with this formula


final concentration before water change=(change between water changes)/(fraction of water change)+amount in replacement water.

So assume something (like nitrates) is increasing at 1 ppm/day.

and the replacement water has 0 nitrates.

and you conduct a 10% water change every week.

final concentration before water change=1ppm/day*7days/(1/10)+0=70ppm


Hey Self: Gee is that why people who do water changes with ro/di water have high nitrates.?
Self: Yep 

The reason is that the amount removed by the water changes must equal the build up between changes.

If you "tie" the size of water change to the interval between changes say 1% water change for every day between changes, the final amount is constant regardless of the schedule used. 10% every 10 days, 20% every 20 days, 30% every 20 days etc all result in 100 ppm just before the water change.

When you add some in the replacement water those values increase by that amount.

This told me why my tanks work. The key is to get the rate of change as close to 0 as possible. I must have been pretty close as my tanks run for years with no water changes. And nitrates/phosphates are always 0 with no water changes and using tap water.

The forumla is so easy to use I don't need spread sheets. But still use them to show how the forumla works.

my .02 with thanks to self.


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## beaslbob (May 29, 2009)

Self says perhaps they are happy you missed it.

*old dude


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## susankat (Nov 15, 2008)

WhiteDevil said:


> Its a good read, I saved the site and will be using it from time to time.
> 
> around here, a response is far and few between unless your thread is deemed argueable then you get all the responses you dont want, mainly from the staff.



I resent that statement! I haven't seen to many arguments here, unless its makes for a good one. One of the main reasons there isn't much response to this is because it is a weekend day and people do have a life other than this forum.

I haven't had a chance to look at it yet. will do that later.

I have done the npt thing before. Had a 75 gal npt. mostly top offs. But I still did a water change in it once every 8 months as I feel the fish and plants do like fresh water. It also helps prevent old tank syndrome. Even Walsted suggest a water change once in awhile.

Most of my tanks now get 50% water change each week, but that is mainly because of the ferts that I use and several of the tanks are for breeding and they seem to breed better when I do the water changes.


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## MOA (Jan 7, 2010)

beaslbob,

For your consideration: http://sites.google.com/site/moashowmanyfish/why-are-water-changes-necessary/water-change-calculator/waterchange1.xls?attredirects=0&d=1

Your sense of humor is amuzing--some good points. Actually, I have been toying with some new formulas that will account for very low frequency water changes. Thanks for the input.

MOA


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