Dilution is the solution to pollution

[scotty333]

For all the noobs and non mathematicians out there,
Did you know it takes 4x25% water changes to reduce nasties or increase goodies by 50%

 

[EricR]

I would've gone with 4x16% water changes ... doh!

 

[Randy Holmes-Farley Verified Community Expert]

For all the noobs and non mathematicians out there,
Did you know it takes 4x25% water changes to reduce nasties or increase goodies by 50%

4x25% water change is equivalent to one 68% water change.

 

[Miami Reef]

4x25% water change is equivalent to one 68% water change.

How do you figure out the math for this?

I want to know much 4x15% water change actually changes.

 

[KStatefan]

How do you figure out the math for this?

I want to know much 4x15% water change actually changes.

Effective Water Change Calculator

Aquarium calculator; Estimate the effective water change amount of several combined smaller water changes.

www.hamzasreef.com

 

[EricR]

How do you figure out the math for this?

I want to know much 4x15% water change actually changes.

48% (rounded)

For non-math people I'd suggest thinking about as what percentage is left after each change,,, so after 15% WC, 85% is left,,, and then multiply that out for each change:
0.85^4 = 0.52 (rounded) so 52% of the original water is left

 

[MoshJosh]

Way easier to just do 1X100% and nip the problem!

 

[Miami Reef]

Thanks guys! I got it figured out. The calculator is also a helpful tool!

I looked online for the formula and I tested it with Randy’s test example from above.

 

[scotty333]

4x25% water change is equivalent to one 68% water change.

Oh dear , did it a different way

I went with a start figure of 10
Then 25% lower is 7.5
Then 5.6
Then 4.3
Then 3.2

Hmm , cocked up my math

 

[BristleWormHater]

Well you could always do a 5x100% water change.

 

[KrisReef]

4x25% water change is equivalent to one 68% water change.

Thanks for correcting the dilution factor!

2x50% WC = 75% dilution.

 

[scotty333]

Well you could always do a 5x100% water change.

Expensive

 

[Randy Holmes-Farley Verified Community Expert]

How do you figure out the math for this?

I want to know much 4x15% water change actually changes.

4x15 —>. .85 x .85 x.85 x .85. =. 0.52

 

[Malcontent]

I often see in freshwater discussions people saying that nitrate will accumulate indefinitely. They sometimes do the math for a few iterations but not enough to see that it doesn't. Then some say you need to periodically do a water change over 50% otherwise it'll accumulate indefinitely.

Sigh.

 

[scotty333]

So for a 100% 25% a time how many ?

 

[EricR]

So for a 100% 25% a time how many ?

Infinite
*that was a mathematical answer, not a practical "close enough" answer, by the way

 

[GSPClown94]

A more generalized formula would be (1 - (1 - x/100)^y) * 100, which should give you the equivalent single water change percentage. Where x is the percent of water being changed and y is the number of times this water change is performed. Or just use the website calculator someone else posted.

 

[Malcontent]

At some point the last original molecule will randomly be changed out.

 

[MoshJosh]

If I wait long enough will the N and P in my tank spontaneously remove itself via Hawkings Radiation. . .

Needless to say my understanding of quantum mechanics is limited . . .

 

[GARRIGA]

Depends at what rate pollutants added vs period between change and why I’ve never placed blind faith on those online calculators. Yes you get X change but if topic is dilution then it gets more complex.