But everyone does water changes...

[reverendmaynard]

<a href=showthread.php?s=&postid=9258451#post9258451 target=_blank>Originally posted</a> by mr.wilson

Once again, I'm not disputing RHF's data or the belief that RWC's can effect a change. My point is, there is proof that they are not cost effective, efficient means of export. There is also data showing that they import impurities into the system that will accumulate. Scientific research and anecdotal observations corroborate the fact that sufficient means of export and supplementation currently exist in a properly set-up reef tank. Water changes are therefore redundant.

I've heard of that kind of "hydro"! :lol: I assumed that you would not charge an expense of that kind towards your reef tank. Although each may aid in the enjoyment of the other, neither is dependant on the other, in most cases. :lol:

I recognize that there are much better methods of export of well studied and tested impurities that collect within a reef system, such as nitrates, phosphates, certain heavy metals, etc. And that water changes for control of these impurities is redundant provided that sufficient export methods are in place to export them at least as fast as they are produced. I agree whole-heartedly that anyone with a consistent nitrate problem that is attempting to use water changes to combat it is fighting a losing battle and would be better served putting their resources towards implementing better methods of export. I would certainly never recommend water changes as a replacement for a known export mechanism, at least with anyone interested in keeping any of the harder to care for coral species. WCs simply aren't effective at reducing a concentration to near zero.

I do disagree slightly with the notion that water changes will introduce problematic levels of impurities either through the water used to make the new water, or the salt mix itself. If the base water is impure, virtually everyone I know is adding more top off water than they are changing water, so if the export methods are not perfect, there is likely to be a greater concentration of that impurity already in the tank. If it's coming from the mix, there should not be a lesser concentration of that impurity in the tank, unless it's being exported by some means, in which case it seems like a moot point (it's being exported, why worry about adding some?)

I don't think we really have much of a diagreement with regards to known impurities and the export methods available to counteract them. My issue is wiith the idea that we know all of the impurities that might be in the water. The bottom line is we don't. Even the most knowledgable scientist in the world, even if we could roll up all the knowledge in the world on the subject into 1 person, that person would still not be able to tell me the exact constitution of the water in my reef tank with any degree of accuracy. Not without running an exhaustive and prohibitively expensive analysis, and even then, with the best testing in the world, wouldn't be able to identify and quantify every molecule and how they interact. A hobbiest armed with his 6 or so test kits knows less than a tenth of a percent about what's in his water. Yet, we run our tests and pronounce everything fine. My position is... Fresh made artificial sea water may not be the absolute best environment possible for our livestock, but I think it's fairly well established that virtually any critter we might choose to keep would be able to thrive fairly well in it. Doing WCs brings your tank back closer to that baseline of known, livable water quality, while not doing any is like running blindfold through a mine field, hoping it's not happening in your tank.

 

[davidryder]

A 1% water change improves water quality by 1% daily, or 30% monthly, assuming there is a deficit. You will only experience greater export than 1% monthly, if the import is less than 1% daily. In other words, a problematic tank with a heavy bioload and poor filtration and husbandry will only be maintained, not reduced by the 1% daily water change. The nitrate load in the model is arbitrary, but falls within a reasonable guesstimate; however, this forum is full of stories of 25% weekly water changes and unshakable 40ppm nitrate.

now you have begun to setup an improvable model with too many unnamed variables. and even if you came up with a somewhat accurate equation that modeled the percentage of water quality improvement through water changes, it would certainly not be linear, as you have described with the formula above. anything involving rates of change will most likely not be linear (mx+b)