Effects of Direct Waterchange VS Continuous

[SomeHappyFish]

Quick Question... Lets say someone does a waterchange of 5G.

You remove 5G then add a new batch of 5G of Saltwater, making sure that new 5G stays in the tank but a continuous waterchange adds a few ML/hours while simultaneously removing the equal amount until the 5G waterchange is done but won't it remove the new saltwater just added in ? Making it less effective?

 

[Garf]

Quick Question... Lets say someone does a waterchange of 5G.

You remove 5G then add a new batch of 5G of Saltwater, making sure that new 5G stays in the tank but a continuous waterchange adds a few ML/hours while simultaneously removing the equal amount until the 5G waterchange is done but won't it remove the new saltwater just added in ? Making it less effective?

Does this help?

Effective Water Change Calculator

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

www.hamzasreef.com

 

[taricha]

Quick Question... Lets say someone does a waterchange of 5G.

You remove 5G then add a new batch of 5G of Saltwater, making sure that new 5G stays in the tank but a continuous waterchange adds a few ML/hours while simultaneously removing the equal amount until the 5G waterchange is done but won't it remove the new saltwater just added in ? Making it less effective?

yes, a little.
Let's say you do a 5g on a 20g system.

scenario 1: 5 gal out, then 5 new gallons in. 25% new water. 75% old water.

scenario 2: at the beginning, the water you are taking out is 100% old water, but by the end it's closer to 75% old water, and so you are taking out a portion of the new water, so you do a little less than otherwise. My brain was blanking on how to work out the exact solution elegantly, so here's the result of brute force calculation. If you change out 5 gallons in a 20 gallon tank, by doing 1/1000 of a gallon at a time....

You end up with 77.88% old water and 22.12% new water at the end. Compared to scenario 1: all out, then all in: 75% old 25% new.

Do you care about that difference? I probably don't.

(If I were having some toxic condition though and I wanted to change 90%+ water, then doing it continuously would leave behind much more than the 10% of the toxic water. So in that scenario I would care. )

 

[SomeHappyFish]

yes, a little.
Let's say you do a 5g on a 20g system.

scenario 1: 5 gal out, then 5 new gallons in. 25% new water. 75% old water.

scenario 2: at the beginning, the water you are taking out is 100% old water, but by the end it's closer to 75% old water, and so you are taking out a portion of the new water, so you do a little less than otherwise. My brain was blanking on how to work out the exact solution elegantly, so here's the result of brute force calculation. If you change out 5 gallons in a 20 gallon tank, by doing 1/1000 of a gallon at a time....

You end up with 77.88% old water and 22.12% new water at the end. Compared to scenario 1: all out, then all in: 75% old 25% new.

Do you care about that difference? I probably don't.

(If I were having some toxic condition though and I wanted to change 90%+ water, then doing it continuously would leave behind much more than the 10% of the toxic water. So in that scenario I would care. )

WOW thanks for doing the math ! The difference is very minimal I woudn't mind the extra % over having less work to do haha.

Thanks !

 

[Randy Holmes-Farley Verified Community Expert]

There are other scenarios that can make AWC even more efficient. For example, taking water out upstream in a sump from where you add it.

IMO, there’s no reason to not do awc out of fear it is less efficient.

I show lots of comparisons here:

Water Changes in Reef Aquaria by Randy Holmes-Farley - Reefkeeping.com