Water change math

Bill Stock wrote:
I'll be setting up an automatic water changer in a few weeks and I've been
having trouble with the math.
The reading I've done suggests that a 20% daily water change is still going
to leave the fish swimming in 82% crap (r = e ^ -.2) as opposed to 50% to
100% crap with large weekly water changes. BUT, the detailed formula I've
seen shows the crap remaining as r=(1-a/n)^n, where a is the percentage of
water changed and n is the number of changes. Now assuming I change 1 gph
and a drop is 1/3600 gallons, then I'm left with 99.99% crap because the
changes are so small. (One drop at a time) Am I missing something here or do
I need to remove some water first to make this work?

I believe you are using a static equation, as there are so many
variables, such as cross circulation vs vertical circulation. I like to
have both types of circulation in an aquarium, except in some breeding
enviroments.
I have only used this type of product a few times (it has been many
years ago, and they may have improved) and found that did not do a good
job of removing a lot of the organic muck that ended up in the nitrogen
cycle.

Carl
http://aquarium-nitrogen-cycle.blogspot.com/

"carlrs" wrote in message
ups.com...

I believe you are using a static equation, as there are so many
variables, such as cross circulation vs vertical circulation. I like to
have both types of circulation in an aquarium, except in some breeding
enviroments.
I have only used this type of product a few times (it has been many
years ago, and they may have improved) and found that did not do a good
job of removing a lot of the organic muck that ended up in the nitrogen
cycle.

Yes, I'm assuming perfect mixing to make my life easy. The overflow will
actually happen in the sump (large plastic barrel). I'm hoping it might act
as a settling chamber as well, since the filter will be after the sump to
allow as much Crap to fall out of suspension before it reaches the filter.

Altum also mentioned the complexity of the variables and in the end I'll
just have to try it. But I thought it made an interesting problem.

Bill Stock wrote:


Yes, I'm assuming perfect mixing to make my life easy. The overflow will
actually happen in the sump (large plastic barrel). I'm hoping it might act
as a settling chamber as well, since the filter will be after the sump to
allow as much Crap to fall out of suspension before it reaches the filter.

Altum also mentioned the complexity of the variables and in the end I'll
just have to try it. But I thought it made an interesting problem.

That sounds like a great way of installing this unit, I never used one
this way.

Carl

"carlrs" wrote in message
oups.com...

Bill Stock wrote:


Yes, I'm assuming perfect mixing to make my life easy. The overflow will
actually happen in the sump (large plastic barrel). I'm hoping it might
act
as a settling chamber as well, since the filter will be after the sump to
allow as much Crap to fall out of suspension before it reaches the
filter.

Altum also mentioned the complexity of the variables and in the end I'll
just have to try it. But I thought it made an interesting problem.

That sounds like a great way of installing this unit, I never used one
this way.

Carl

We'll see what I've forgotten in a few weeks. I'm going to install a couple
of float valves, one to shut of the water if it gets too high and one to
shut off the pump if the water gets too low.

I was going to add the water to the bottom and take the effluent off the
top. But NetMax suggested plumbing my overflow to the bottom and adding the
water to the top. I should get more crap sucked out the overflow that way.
I'm not sure how much it will help, but it sounds good in theory.