Water Changes - the mathematical bit!

wtpdosa said:
One of the things that I have read recently about water change percentages is that the larger the percentage of change, the more stress the change causes your tanks inhabitants.
Another way to think of changes is maybe:

10% very little stress
20% little stress
30% a little more stress
40% definate stress
50% disruptive stress
on up percentages... can eventually cause death.
It doesn't take a mathematician to figure out that increased stress kills.

My tank friends are very important to me and as far as I'm concerned,
the less stress I put on something I enjoy, the better it is for me and my fishy friends. If your too lazy or don't give a hoot, do yourself and your fish a favor and take them back to the store you got them from, sell your equipment and find something else that doesn't stress you out.
Click to expand...
Totally disagree.

If a 50% water change was so bleeding stressful, then why do the rainbowfish in all my tanks either try to swim up the Python hose while I'm doing it or play in the current? Nobody runs. Nobody hides.

Not to mention the fact that the minute I'm done they start spawning regardless of the time of day?

A waterchange is low lights, champagne, and Barry White to rainbowfish.

I'll take the "stressful" 50% twice a week, thanks :)

Roan
 
5.gif


Randy the rainbow says......"What.....Only TWICE a week ??
sad0127.gif
"
 
Last edited:
wtpdosa said:
One of the things that I have read recently about water change percentages is that the larger the percentage of change, the more stress the change causes your tanks inhabitants.
Click to expand...

Keep in mind that most fish in their native habitats are in water that is constantly being refreshed - the basic parameters are the same, but, as it flows around them, pollutants are being better dealt with than we could ever possibly achieve in even the largest tank with the best filtration. The real stress comes from the toxics that build up, not from treated water changes. As I stated above, I do weekly 50% water changes - in over 35 years, I cannot think of a fish loss that I could relate to a water change. On the contrary, activity and color are usually at its best those first several hours or few days afterwards. Furthermore, I frequently have spawns after a water change. As stated above in another earlier post, the only time a large water change can be problematic is when your fish are not use to such a regimen. If you decide to change the volume and/or frequency of your water changes, then build up slowly over several weeks. There are some tanks that I do smaller changes in, such as my reef tank. Overall, however, in my personal opinion and in 37 years of fish keeping experience, I believe that significant and frequent water changes are the single most important aspect of truly successful fish keeping.
 
OK - now I'm confused :confused:

I read the article at http://www.thepufferforum.com/artic...changemath.html and I agree completely with it. It's looking at a different issue from what I wrote, though.

My post:
Suppose I've decided I want to change 25 gallon of water per week, from my 50 gal. I wanted to find out how much difference it makes whether I do one 25 gallon change (50%) or five 5 gal changes (5 lots of 10%). What I found out was that the overall levels of, say, nitrates will remain about the same whichever way I choose. The graph attached to my first post shows the actual day-by-day differences between the approaches.

thepufferforum article (linked above):
This article is looking at something completely different. It's looking at the differences between doing a 10% water change every week or doing a 50% water change every week. (Naturally, it's saying that 50% is better!) It's a good article and I agree with what it says. There's no contradiction between what I wrote and what's in this article: they're about different things. (btw - Roan Art said this article is by RTR. Is it the same RTR that's posting in this thread? :confused: )

What I'm puzzled about is this:
RTR said:
A 10% daily change for 5 days serially is not equal to a 50% change on day 5. Over time the differences become highly significant.
Click to expand...
If it's not the same, what's the actual difference? According to this statement, my info in the first post is completely wrong. I've been wrong before, and if I've made a mistake I'll be happy to learn better :) - but you'll need to tell me why the two approaches are not the same!
 
patoloco said:
I posted this thread time ago where I used my non so mathemathical skills to try to explain the stuff. Please read

http://www.aquariacentral.com/forums/showthread.php?t=69989
Click to expand...
Aren't spreadsheets cool??? If I'd found this post before, I would have just added my 2 cents to that! I used exactly the same approach as you, but then tried a few scenarios to find the effect of different frequency and quantity of water change on stabilization levels. Neat!
 
I found the nitrates will tend to stabilize in an amout that's very much described as your nitrate production (how much your fish raise the nitrate level every -let's say- week) and the amount of nitrates you have in yuour tap water.

The only difference will be how long it will take to stabilize.

My conclusions:

- Larger water changes will stabilize the nitrate count faster (you will take less time to see your tank steadily at a given amount of nitrates).

- More frequent water changes will stabilize a lower nitrate: if you change the water every week, you'll have a normal nitrate level worth a week of bio activity. A monthly water change, normal nitrate level will be the same of a whole month of production.

- Larger and more frequent WC, result in a lower nitrate concentration that becomes stable in less time.
 
csdax said:
(btw - Roan Art said this article is by RTR. Is it the same RTR that's posting in this thread? :confused: )
Click to expand...
Yesssssssssssssssh. 'Tis he. Da man :)

Btw, I'm from Guelph ;)

Roan
 
Here's how I see it and I'm sure David Boruchowitz would agree with me because it comes from his book.

A 50% water change every 5th day removes more old water than a 10% water change every day.

Here's the logic.

Say you have 100gal. and remove 50% of the water. You are left with 50gal. new water and 50gal. old water.


If you take the same 100gal. and remove 10% of the water. You are left with 90gal. old water and 10gal. new water.

The 2nd day you remove 10% more and you are really only removing 9gal. of the oldest water (as you can not physically only remove the oldest water as it mixed with the new water yesterday). You are left with 81gal. old and 19gal. new.

The 3rd day you remove 10% more and are actually removing 8.1 gal. of oldest water. Left with 72.9gal. old and 27.1gal. new.

The 4th day you remove 10% more and are actually removing 7.29 gal. of oldest water. Left with 65.61gal. old and 34.39gal. new.

The 5th day you remove 10% more and are actually removing 6.46 gal. of oldest water. Left with 59.15gal. old and 40.85 gal. new.

As you can see the one 50% water change actually removes more of the oldest water because it is inevitible that when you do a water change you are also removing some of the newer water along with it.
 
You must log in or register to reply here.
AquariaCentral.com
Top Bottom