Water change calculations

[Crabby48]

I am switching salts and keeping track of how many 10% weekly water changes need to be done to replace 100% of water using a calculator. I am 9 weeks in but want to do a 20% change but not sure how to figure it out after doing 10 % changes.

Is ther a math quation to figure it out and how do I figure out the next week if I go back to 10% water change?

 

[Quietman]

I am switching salts and keeping track of how many 10% weekly water changes need to be done to replace 100% of water using a calculator. I am 9 weeks in but want to do a 20% change but not sure how to figure it out after doing 10 % changes.

Is ther a math quation to figure it out and how do I figure out the next week if I go back to 10% water change?

Hamza's Reef

www.hamzasreef.com

Very handy calculators.

 

[ScottB]

I am switching salts and keeping track of how many 10% weekly water changes need to be done to replace 100% of water using a calculator. I am 9 weeks in but want to do a 20% change but not sure how to figure it out after doing 10 % changes.

Is ther a math quation to figure it out and how do I figure out the next week if I go back to 10% water change?

Haha. I just did this quick/dirty worksheet to calculate for AWC for someone else here yesterday. (I was pre-gaming, but it looks correct to me.) The outlined boxes you can change inputs for. You are wise to go slowly, but as you can see after a couple dozen WCs you are 99%. Heck, with 5 more 20% WCs you are at 90%.

If you are going to alternate or change often this could get clunky to manage the formulas. You can see my change at period 10 if you look at the cell references.

 

[beaslbob]

actually you'll never get to 100%.

90% of the water remains with 10% new.
then 90% of the 90% for 81% and 19% new

and so on

so try .9 raised to n where n is the number of water changes. then new water is 1- .9^n

if n is 20.

old is .9^20= .121577 new .8784

or using excel

 

[beaslbob]

Another consideration is parameters which are linear will build up to where amount of build up (or depletion) is removed by the water change. So that the value before the water changes is the parameter change/fraction of water removed.

For example if something is increasing at 1ppm/day and you do a 10% water change every week you get:

1ppm/day*7days/(1/10)

7ppm/(1/10)=70ppm

the tank will wind up at 70ppm before the water change, drop down to 63ppm then rise to 70ppm before the next water change.

That also assumes there is 0ppm in the replacement water. Both values increase by the value in the replacement water. Assuming 100ppm in the replacement water the before water change goes to 170ppm then down to 163ppm and back up to 170ppm before the next water change.

hopefully that is not too confusing. it only took me about 40 years to come up with that. LOL

my .02

 

[Randy Holmes-Farley Verified Community Expert]

Remember that export calculations do not apply to phosphate because such a large amount is temporarily held bound to the surfaces of rock and sand.

 

[Crabby48]

Hamza's Reef

www.hamzasreef.com

Very handy calculators.

That is the website I use for calculators. Very handy

Haha. I just did this quick/dirty worksheet to calculate for AWC for someone else here yesterday. (I was pre-gaming, but it looks correct to me.) The outlined boxes you can change inputs for. You are wise to go slowly, but as you can see after a couple dozen WCs you are 99%. Heck, with 5 more 20% WCs you are at 90%.

If you are going to alternate or change often this could get clunky to manage the formulas. You can see my change at period 10 if you look at the cell references.

Thanks that is very cool.

actually you'll never get to 100%.

90% of the water remains with 10% new.
then 90% of the 90% for 81% and 19% new

and so on

so try .9 raised to n where n is the number of water changes. then new water is 1- .9^n

if n is 20.

old is .9^20= .121577 new .8784

or using excel

Another consideration is parameters which are linear will build up to where amount of build up (or depletion) is removed by the water change. So that the value before the water changes is the parameter change/fraction of water removed.

For example if something is increasing at 1ppm/day and you do a 10% water change every week you get:

1ppm/day*7days/(1/10)

7ppm/(1/10)=70ppm

the tank will wind up at 70ppm before the water change, drop down to 63ppm then rise to 70ppm before the next water change.

That also assumes there is 0ppm in the replacement water. Both values increase by the value in the replacement water. Assuming 100ppm in the replacement water the before water change goes to 170ppm then down to 163ppm and back up to 170ppm before the next water change.

hopefully that is not too confusing. it only took me about 40 years to come up with that. LOL

my .02

Thanks for the info. I will have to sit down and read it a few times to process it but you brought up thing I never thought about