unclejed

I felt it was time to debunk the myth about water changes. From this and the other forums I am a member, I am amazed how many people suggest a water change to accomplish everything from lowering Nitrates to curing a Coral. The article you will read will put to rest the idea that water changes can accomplish these things, or it should if you keep an open mind to the actual physical occurrence that happens when you do a water change. Although the article is focused on why water changes do not effectively keep nitrates under controll, let alone eliminate them, you will see the minimal effect they have and why a water change will not cure anything in and of itself. Happy reef keeping!
http://www.fishyou.com/fish-nitrates-water.php

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"There is no nonsense so gross that society will not, at some time, make a doctrine of it and defend it with every weapon of communal stupidity.
Robertson Davies

Don Trinko

Ok ; I will read the artical but... If your nitrates ar 40 and you change 50% of the water the nitrates are 20? At least till the biofilter produces more? Don T.

Ok; I read the article. I have discus, in my discus tanks I change 50% twice a week. The nitrates are less than 5. I have othe FW tropicals. I change 25 % once a month. The nitrates are typicaly 40. If the get much higher than 40 I change more water and the nitrates go down.
If you do not do WC in fresh water the nitrates will keep going up unless you have plants or other means of removing nitrates. I realize SW is somewhat different. You can have a refugum with plants and light 24/7 but for most of us the simplest way to lower nitrates is WC.
You can argue that most people do not change enough water but IMO you can not say that WC does not reduce nitrates. Don T.

RJRofFL

I, too, have read the article and I have to say that I personally disagree with it.

It should be noted first, that this site, "FishYou.com" promotes and appears to be a site offering (and I quote) "Alternative Fishkeeping." It further states "original and unconventional methods of aquaria." "substantial volume of research are from non-english sources." and further announces (in capital letters) "USE ALL INFORMATION AT YOUR OWN RISK."

I am by no means "blasting" or "bad mouthing" this, as everyone is entitled to their opinions and methods, especially in this hobby. I just feel that the above should be noted, and the article not taken as "gospel."

That said, and although there is a degree of truth in the article which focuses on the ineffectiveness of water changes to "eliminate" or "control" nitrates, it does, at least acknowledge elsewhere that a buildup of nitrates can reach dangerous levels if left unchecked.

It is my feeling and belief that regularly scheduled performed water changes can and will reduce nitrates to a safe and less toxic level.

However, it is also my belief that water changes offer far more than simply reducing nitrates. Eliminating or postponing water changes will have an adverse effect on the aquarium by:

A buildup of nitrates (thru lack of WC) can reduce the alkalinity resulting in a pH drop.

Phosphates, pheromones and other chemicals can build up as well.

The necessary minerals and trace elements become depleted over time, resulting in a GH drop.

And finally, poor water quality (from not being changed) obviously will put stress on fish, lead to infection to a wounded fish, and often becomes a cause for fungus and/or parasite problems.

Additionally, water changes supply clean oxygenated water, essential to maintaing healthy livestock.

So, it is my feeling that water changes offer far, far, more positive effects to our aquariums.

Bob

lostanime

+1 on above.

Reduce pollution by dilution...

With that being said, common sense will substantially reduce the required volumes and frequency of water changes (under-stocking, good skimming, measures for nutrient export such as macro-algae)... but as aquarists we cant test for and don't even fully know all of the things that are accumulating in our tanks. Water changes are a great safety net to keep both the things we do and the things we dont test for in check.

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Lots of little tanks here and there.

jzmckay

I just emailed the administrator of that site. The argument is fundamentally flawed, since he assumes a 50% water change at the same frequency of his rate of production, resulting in a false conclusion. If he chose a different size water change or a different frequency, it would give different results.

I've attached a copy of the email I sent him. See below for an explanation of the errors, and also for an equation that can be used to estimate stable nitrate levels given constant parameters.

One thing to note from that equation is that varying the frequency and/or amount of water changes can have unexpected consequences. I suggest playing around with various values a bit to find the optimal solution for your setup.

For example, the equation clearly shows that a 25% water change every week will result in a HIGHER average nitrate level than a 50% water change every two weeks. More frequent is not necessarily better. It depends on the size of the changes.

To get an equivalent average nitrate level to a 50% water change every two weeks, you'd have to do about a 30% water change every week. Perhaps it doesn't seem like a major difference, but depending on your bioload, such distinctions could make the difference between a sick tank and a healthy one.

[Appended message follows]
------------------------
First, I'd like to thank you for being one of the few resources on the web to note that water changes don't necessarily have the impact on nitrates that we might expect. This is terrific info, and people need to think about their calculations more closely.

That said, I think your particular example (a 50% water change) is not well-chosen. You conclude that: "Water changes does not control nitrate, but only slows down the rate of increase, normalising at the level that it is produced."

To me (and I think to the average reader), that implies that water changes always normalize at the production level of nitrates. In your example, the production level is 10. The level after weekly water changes seems to be trending toward 10. A naive reader might conclude that no matter how you change the water, it will trend toward the production level.

However, that is false. For example, if you only do a 25% weekly water change with a weekly production of 10 ppm, the nitrate level will stabilize around 35 ppm (40 ppm before water change, 30 ppm just after water change; since the values will move between these extremes between water changes, the average is 35 ppm).

Here's a little table of average nitrates, assuming various sizes of weekly water changes for a production of nitrates at 10 ppm/week:

Water change % - Average NO3 (ppm)
0% - infinite
5% - 195
10% - 95
15% - 61.67
20% - 45
25% - 35
30% - 28.33
35% - 23.57
40% - 20
45% - 17.22
50% - 15
55% - 13.18
60% - 11.67
65% - 10.38
70% - 9.29
75% - 8.33
80% - 7.5
85% - 6.76
90% - 6.11
95% - 5.53
100% - 5

Similarly, the frequency of water changes will alter the average nitrate level. Assuming a production of 10 ppm/week, and 25% water changes, the nitrates would be the following on average, depending of the frequency:

Frequency - Average NO3 (ppm)
daily - 5
every other day - 10
semiweekly - 17.5
weekly - 35
biweekly - 70
monthly - 140
bimonthly - 280
quarterly - 420
semiannually - 840
annually - 1680
never - infinite

Given these charts, I think it is safe to say that water changes *DO* reduce average nitrate levels when done on a regular basis. If you had a nitrate production of 10 ppm/week and nothing to absorb it, you'd build up to lethal levels over a couple of months. (In practice, this usually takes longer, because some nitrates get absorbed or processed in various ways.)

In other words, you are correct about a couple things:

(1) Without doing 100% water changes, you'll never reach zero nitrates without something to absorb them.
(2) If you have too much nitrate production in your tank, you'll never be able to reduce it to reasonable levels only by water changes.

However, it is COMPLETELY WRONG to say that the size and frequency of water changes won't have a significant impact on whether the nitrate level in your tank is high or low. If you do rather large water changes on a frequent basis, you will reduce nitrates. If you do very small changes on an infrequent basis, you'll build up nitrates. That's what the math says.

One other factor -- you assume that the nitrate level in the replacement water is ZERO. This is generally not the case. For example, a 10 ppm/week NO3 production with weekly 25% changes will normally stabilize at an average level of 35 ppm, as stated above. If the level of nitrates in the replacement water is 5 ppm, the stability point will also be increased to 40 ppm.

To summarize the above tables in the simple model that you assumed on your page, here's a formula to calculate average nitrate level:

Average NO3 level =

w + {N * t * [(100 / p) - 0.5]}

where,
w = NO3 level in replacement Water
N = Nitrate production per week (net)
t = Time between changes (in weeks)
p = Percentage of water changed each time

Of course, N can be increased by more fish, and decreased by things like plants, as you say. It is here assumed to be relatively constant. But t and p will impact average nitrate levels. Thus, water changes will never reduce nitrates to zero, but they will manage the levels depending on t and p. (In a real aquarium, as the average level of NO3 changes, of course the net production of new NO3 will be affected, since bacteria, algae, plants, etc. will change growth rates, so the equation is not this simple.)

And, of course, without a drastic nitrate management through other means in a tank, you won't be able to sustain a NO3 level below the replacement water you are using, another point that is often forgotten.

jzmckay

By the way, you shouldn't just believe me and the equation. Do the math, just as he shows on his webpage. Just change the rate of NO3 production or the size of the water changes. You'll quickly see that the amount of nitrates will converge to the result given by the equation in my previous post.

Or, rather, you'll see that even the webpage is deceptive, since it implies that the average NO3 level converges to the level AFTER the water change. Which is of course false. That's the level after the water change, which would be the lowest NO3 level in his example. The AVERAGE nitrate level would be midway between the level BEFORE and the level AFTER the water change, which is what my formula calculates.

By the way, using the same variables, the max/min nitrate levels can be calculated.

Maximum NO3
= w + [N * t * (100 / p)]

Minimum NO3
= w + {N * t * [(100 / p) - 1]}

Obviously, the Max NO3 is the number you most want to be worried about, though in a healthy tank, you hopefully shouldn't see a huge difference between the MAX and MIN.

unclejed

Well, it seems most have missed the point. I said; "I am amazed how many people suggest a water change to accomplish everything from lowering Nitrates to curing a Coral. I am amazed how many people suggest a water change to accomplish everything from lowering Nitrates to curing a Coral." There is a lot in between the Nitrate issue and "curing a Coral". Where I was going with this is that I will read a post of a Coral having problems and right away you get the "do a water change" crowd piping in. Water changes have their place, but the point is they have a relatively minimal effect on over all water parameter stability. We must address the real causes of the inherent issues that come up in our tanks and not simply rely on water changes to accomplish these thing for us. You can use them as band aid if you like until you establish what the problem is but a water change is in no way a cure really for anything. The premise of doing a 50% water change, for example, to bring down nitrates is potentially destructive and at the least disruptive to the tank environment. Depleting nutrients and bacteria from the water column can have undesirable effects. In a fish only tank you may get away with it but you are risking the overall health of a reef tank. The point here is to get everyone to exercise prudent husbandry and maintenance as the best measure of keeping a healthy aquarium.

__________________
"There is no nonsense so gross that society will not, at some time, make a doctrine of it and defend it with every weapon of communal stupidity.
Robertson Davies

Jay

This is a great thread...I am going to put it up on the Front Page.

I have some requests, but I will have to post them tomorrow.

Jay

louistheloach

I thought we couldn't post links to other forums like this?

I had one of my links removed from a site that was no different than this one. Is there a double standard?

ltl

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unclejed

I am personally unaware of that happening. If a Moderator or administrator did, maybe they will respond here as to their reason for doing so.

__________________
"There is no nonsense so gross that society will not, at some time, make a doctrine of it and defend it with every weapon of communal stupidity.
Robertson Davies