Constant water change vs Regular water changes
- Thread starter gimmito
- Start date
Eight
Guest
rygh said:
I don't quite understand this statement... Doing a continuous water change from a math perspective is very little different than doing a large single change. You have the additional benefits of decreased stress to livestock and reduced effort. Cons are primarily $$$ for equipment and the possibility of a mechanical problem. See Randy Holmes-Farley's article and calculations here:
http://reefkeeping.com/issues/2005-10/rhf/index.php
"These changes are slightly less efficient than single batch water changes of the same total volume. A continuous water change of 30% exactly matches one batch 26% water change. As with very small batch water changes, these have the advantage of neither stressing the organisms (assuming the change is done reasonably slowly), nor altering the water level in the aquarium. The ease of doing such changes automatically also makes it far more likely that busy or lazy aquarists will actually do them."
I use a system identical to Tong's and it's one of the best investments I made for my setup.
Jason
rygh
Guest
Hi,
Not really sure about that article. I may check more when I have time.
I figured I might be off on the math, so I wrote a brain-dead C program.
It assumed a 100ppm of whatever bad thing to start with.
Run 2 times, at 30% change each
Pollutant = 100.00
After 1 = Pollutant = 70.00
After 2 = Pollutant = 49.00
Run 10 times, at 3% change each
Pollutant = 100.00
After 1 = Pollutant = 97.00
After 2 = Pollutant = 94.09
After 3 = Pollutant = 91.27
After 4 = Pollutant = 88.53
After 5 = Pollutant = 85.87
After 6 = Pollutant = 83.30
After 7 = Pollutant = 80.80
After 8 = Pollutant = 78.37
After 9 = Pollutant = 76.02
After 10 = Pollutant = 73.74
49->73 us a big difference.
But less than a factor of two, and it never gets that much worse at 0.3%, etc.
So you give up that factor in efficiency (And thus cost for salt/water), but gain hugely in labor efficiency.
So after thinking more, might be worth it.
main()
{
int i;
float tank_bad;
tank_bad = 100.0;
printf("nRun 2 times, at 30%% change each n");
printf("Pollutant = %.02fn",tank_bad);
for (i=0; i
Not really sure about that article. I may check more when I have time.
I figured I might be off on the math, so I wrote a brain-dead C program.
It assumed a 100ppm of whatever bad thing to start with.
Run 2 times, at 30% change each
Pollutant = 100.00
After 1 = Pollutant = 70.00
After 2 = Pollutant = 49.00
Run 10 times, at 3% change each
Pollutant = 100.00
After 1 = Pollutant = 97.00
After 2 = Pollutant = 94.09
After 3 = Pollutant = 91.27
After 4 = Pollutant = 88.53
After 5 = Pollutant = 85.87
After 6 = Pollutant = 83.30
After 7 = Pollutant = 80.80
After 8 = Pollutant = 78.37
After 9 = Pollutant = 76.02
After 10 = Pollutant = 73.74
49->73 us a big difference.
But less than a factor of two, and it never gets that much worse at 0.3%, etc.
So you give up that factor in efficiency (And thus cost for salt/water), but gain hugely in labor efficiency.
So after thinking more, might be worth it.
main()
{
int i;
float tank_bad;
tank_bad = 100.0;
printf("nRun 2 times, at 30%% change each n");
printf("Pollutant = %.02fn",tank_bad);
for (i=0; i
rygh
Guest
DOH. H)
All that, and it had a really obvious stupid mistake. (Busy doing my real job I guess)
I ran the first twice as much.
Doing it correctly, if just run for 30% / 10 x 30%.
The results are 70% versus 76%. Not much.
HOWEVER:
You do more than one 30% change, and now I think I understand what the article did wrong.
But this time I am going to check my math first before posting.
All that, and it had a really obvious stupid mistake. (Busy doing my real job I guess)
I ran the first twice as much.
Doing it correctly, if just run for 30% / 10 x 30%.
The results are 70% versus 76%. Not much.
HOWEVER:
You do more than one 30% change, and now I think I understand what the article did wrong.
But this time I am going to check my math first before posting.
rygh
Guest
Ok, now I get it.
Basically, the issue is comparing a single 30% versus 10 x 3%.
In actuality, you keep changing the water, forever.
Fixed example, starting at 100:
After 10 x 30%, pollutant = 2.82
After 100 x 3%, pollutant = 4.76
Mathematically could be 1.7X, or could be +1.94
It also make a noticeable difference on how long it takes to dilute.
Say you want that 100ppm to get to 10ppm.
It takes 6 changes at 30%
It takes 75 changes at 3%. (So use 7.5 to compare)
Noticeable mathematically, but far from large.
Basically, the issue is comparing a single 30% versus 10 x 3%.
In actuality, you keep changing the water, forever.
Fixed example, starting at 100:
After 10 x 30%, pollutant = 2.82
After 100 x 3%, pollutant = 4.76
Mathematically could be 1.7X, or could be +1.94
It also make a noticeable difference on how long it takes to dilute.
Say you want that 100ppm to get to 10ppm.
It takes 6 changes at 30%
It takes 75 changes at 3%. (So use 7.5 to compare)
Noticeable mathematically, but far from large.
rygh
Guest
From a math standpoint:
It is great for adding the good stuff. Calcium/salt/etc.
It is terrible for removing the bad stuff. Nitrates/etc.
The difference is in adding a constant amount versus diluting a certain percentage.
* NEW UPDATE:
* As I learned after doing it in detail, just thinking in math terms can fool you.
* While the numbers can be different, in terms of what you care about, it is actually pretty similar.
It is great for adding the good stuff. Calcium/salt/etc.
It is terrible for removing the bad stuff. Nitrates/etc.
The difference is in adding a constant amount versus diluting a certain percentage.
* NEW UPDATE:
* As I learned after doing it in detail, just thinking in math terms can fool you.
* While the numbers can be different, in terms of what you care about, it is actually pretty similar.
