What does X% water change mean?

[scolley]

Sorry for the terribly newbie question, but I'm trying to plan out all the support equipment for my first tank BEFORE I set the tank up. So I'm working through various needed storage capacities for RO/DI water, and mixed salt water for water changes. But I've run across something that I cannot find the answer too...

When someone states that they do an X% water change at Y frequency, what does X% refer to?

Is that a percent of their unfilled tank volume? Nominal tank volume (unfilled volume minus the space taken up by rock, fish, etc.)? Or is it a percentage of overall system volume (unfilled tank + sump + water in lines, etc.)?

The difference between these can be pretty significant.

Thanks in advance!

[der_wille_zur_macht]

Most people probably interpret it to mean % of the display tank's total volume. Perhaps this is not the most "correct" interpretation, but it's the most common.

That said, for the most common tank configuration (around 1 lb/gallon of live rock and a sump that's around 30 - 40% display tank volume) it's probably about the same as % of actual water volume in the system.

[Aquarist007]

Originally posted by scolley
Sorry for the terribly newbie question, but I'm trying to plan out all the support equipment for my first tank BEFORE I set the tank up. So I'm working through various needed storage capacities for RO/DI water, and mixed salt water for water changes. But I've run across something that I cannot find the answer too...

When someone states that they do an X% water change at X frequency, what does X% refer to?

Is that a percent of their unfilled tank volume? Nominal tank volume (unfilled volume minus the space taken up by rock, fish, etc.)? Or is it a percentage of overall system volume (unfilled tank + sump + water in lines, etc.)?

The difference between these can be pretty significant.

Thanks in advance?

Its a percentage of your overall system volume.

eg My system is about 225gal so I do about 15 per cent of that every two weeks or about 30 gal
so I pump out 30 gals of water from the sump and add 30 gals of newly prepared salt water back to sump which is the same salinity and temp of my system

BTW
it should be x% water change at y frequency since they are two different variables

[scolley]

Originally posted by capn_hylinur
BTW
it should be x% water change at y frequency since they are two different variables

WOW! Do I feel like a dufus!

Believe it or not, I did have it that way when I first composed the question, but I had x and y in lower case. When I went back to change them to upper, clearly I screwed up and put X's everywhere! Sorry.

I've changed it in the original post, as I don't want to confuse people reading the thread. But good catch cap'n. Thank you.


Now... the two responses so far confirmed my suspicion - that there may not be a clear and universally agreed convention. X% means different things to different people.

Though as long as some significant portion of the well informed community consider X to be total system volume, caution dictates that whatever what change percentage I choose to adopt, my capacity should err on the conservative side and provide sufficient capacity to change X% of total system volume.

Thanks folks... gonna need a bigger bucket.

[dots]

http://reefkeeping.com/issues/2005-10/rhf/index.php

Here is some information to help you determine your needs.

[scolley]

Thanks Douger, that is an EXCELLENT article. I've read previously, but it is definitely worth pointing out to any and all newbies.

And within the context of that article, when Melev refers to X% water change, he is clearly referring to the total volume of water in the system - nominal tank volume + sump + plus + water in lines and other equipment.

Where my problem lies is in determining what size containers I'll be using, because that is dependent upon what % of water I plan to change over time. And as I try to make that determination, I research tanks that appear to me to be successful. And when I check to see what % water changes they perform, I rarely get an indication of what that percentage is referring to (tank vs. nominal tank vs. system volumes).

So yes, Melev is definitely referring to the total volume of water in the system (otherwise his math falls apart). But I don't know what other people are referring to when they say "I change X% at Y frequency." And the first two post here demonstrate that there may well not be a clear consensus.

[dots]

The main point is.....do it in the first place, and do it regular enough and in large enough quanties.....your corals and fish are not going to feel slighted, by a few percentage either way.

As far as total versus display......most sumps volumes offset the displacement of LR/LS in a system, remembering that LR is porous.......no need to make it more complicated unless you have a super small or large sump volume.

The main idea to come away with....set up plan, and follow it be it: weekly, bi weekly, montly...etc, and adjust as you see fit.

But just do it and be religous about it is what I stress here.

For you......most use a 55 gallon trashcan to collect and mix the water.....which is about 30% of 180g...........looks like a good place to start.

[Aquarist007]

Originally posted by dots
The main point is.....do it in the first place, and do it regular enough and in large enough quanties.....your corals and fish are not going to feel slighted, by a few percentage either way.

As far as total versus display......most sumps volumes offset the displacement of LR/LS in a system, remembering that LR is porous.......no need to make it more complicated unless you have a super small or large sump volume.

The main idea to come away with....set up plan, and follow it be it: weekly, bi weekly, montly...etc, and adjust as you see fit.

But just do it and be religous about it is what I stress here.

For you......most use a 55 gallon trashcan to collect and mix the water.....which is about 30% of 180g...........looks like a good place to start.

I actually use two plastic garbage cans--one for ro/di and one for salt--never hurts to have lots of ro/di water around

[PRDubois]

Bottom line is:

10-15% each week

or

20-30% every 2 weeks

[scolley]

I really appreciate all the guidance folks. But I'm getting questions answered that I'm not asking. I'm not looking to know how much of water I should change. Nor the frequency. Nor what size container I should use. Nor how I should go about it. Those are all VERY important answers - but they do not answer the simple question that I'm asking right now.

I just want to know when someone says "I change X% of my water on a Y basis", what do they usually mean by X?

Easy question. The first two responses answered that question, so as far as I can tell, there is no consensus on the answer.

[jrice0309]

"I just want to know when someone says "I change X% of my water on a Y basis", what do they usually mean by X?"

For example:

I have a total of 70 gallons total in water volume including sump.

I do a 15% water change every 2 weeks.

15% of 70 gallons is 10.5 gallons.

So, every 2 weeks, you would take out 10.5 gallons of water from your tank, and replace it with 10.5 gallons of new saltwater.

Does this answer the question?

[der_wille_zur_macht]

Originally posted by scolley

I just want to know when someone says "I change X% of my water on a Y basis", what do they usually mean by X?

That was more or less my point, but I guess it was obscured. There is no consensus, so when someone dictates their X and Y variables to you, you should ask for clarification if you want to be precise.

If we were all going to sit down and agree on a standard, it probably should be % of total system volume, but IME when you probe most people, especially newbies, with average mixed reef tanks, you'll find they are basing it off DT total volume. (The same way we typically base other "rules of thumb" off DT total volume, i.e. 1 lb of rock per gallon, etc.)

At any rate, it's probably more or less a moot point, because there isn't even an agreed-upon "best practice" for water changes, beyond some (more or less unjustified) rules of thumb like the ones you're seeing in this thread. These rules-of-thumb are probably fine goals, but they are based on tradition and anecdotal evidence. There's no clear theory behind them other than "it's always worked for me that way," and there is no master equation that will find an optimal water change schedule for a given set of parameters.

[Aquarist007]

Originally posted by der_wille_zur_macht
That was more or less my point, but I guess it was obscured. There is no consensus, so when someone dictates their X and Y variables to you, you should ask for clarification if you want to be precise.

If we were all going to sit down and agree on a standard, it probably should be % of total system volume, but IME when you probe most people, especially newbies, with average mixed reef tanks, you'll find they are basing it off DT total volume. (The same way we typically base other "rules of thumb" off DT total volume, i.e. 1 lb of rock per gallon, etc.)

At any rate, it's probably more or less a moot point, because there isn't even an agreed-upon "best practice" for water changes, beyond some (more or less unjustified) rules of thumb like the ones you're seeing in this thread. These rules-of-thumb are probably fine goals, but they are based on tradition and anecdotal evidence. There's no clear theory behind them other than "it's always worked for me that way," and there is no master equation that will find an optimal water change schedule for a given set of parameters.

I agree
also since everone's tank is a different from the next person's tank they will have a unique set of varibles dictating when and how much they do water changes.
One of the biggest reasons for doing a water change is to replace trace elements that are used up by corals ect in the ecosystem.
Corals are different in the demands they put on these trace elements also.

Then there are always the unplanned situations that arise where an immediate 30 per percent or more of a water change is needed
eg a spike in nitrates
or an overflow or flood ect----those darn snails in my fuge usually end up getting stuck in the drain pipe and I come down to the basement to find water all over the floor

I suggested above that I keep one 35 gal pail with salt water made up at the tank temperature and 2 25 gal pails or ro water already made up just in case

[Fizz71]

I'll keep my answer to your original question to further your consensus.

When I think about % change I take a guess at my system's total water capity. I have a 240g display tank and a 100g sump but I have a DSB in the sump and don't run it up to the rim, and neither is my tank. So I do my math based on a 300g system.

I have a 55g drum of SW mix and a 55g drum of RO. I never fill the drum to the lid or suck it dry so I round it all to 50g water change whenever I do it. So I'm looking at a 17% water change whenever I pull the trigger.

[KarlBob]

Just to add another data point for you, here's what I do:

I don't have a sump on either of my tanks, and I don't have the foggiest idea how much water is displaced by my live rock and sand, so I go by the unfilled volume of each tank (Option A from the original question). For me, a 10% water change means 10 gallons - 8 gallons in my 80 gallon tank, and 2 gallons in my 20 gallon tank. That works out pretty nicely, since I run my RO/DI system into 5 gallon jugs.

Come to think of it, I do have a hang-on-tank (HOT) refugium, but it only adds a couple of gallons to the 80 gallon tank. My HOT protein skimmers (Aqua C Remora and Remora Pro) add a few more gallons. Hmm, something to think about... but I'll probably continue doing the same thing.

[scolley]

First... I appreciate everyone's feedback. Thank you!

But due to the PITA of responding to multiple quotes here (some forums have an easy way to respond to multiple quotes that I have not seen here), I'll respond to only a couple. Sorry for not responding to more (maybe RC will see fit to install the "multiple quotes" vBullitin option some time in the future... and catch up to the rest of the forum world)

Originally posted by der_wille_zur_macht
If we were all going to sit down and agree on a standard, it probably should be % of total system volume, but IME when you probe most people, especially newbies, with average mixed reef tanks, you'll find they are basing it off DT total volume. (The same way we typically base other "rules of thumb" off DT total volume, i.e. 1 lb of rock per gallon, etc.)

Understood. Thank you. From my newbie observations, I'm inclined to suspect the same... newbies generally referr to empty tank volumes, with more sophisticated reefers referring to total system water volume. Thanks.

Originally posted by der_wille_zur_macht
At any rate, it's probably more or less a moot point, because there isn't even an agreed-upon "best practice" for water changes, beyond some (more or less unjustified) rules of thumb like the ones you're seeing in this thread.

Agreed. And while my goal remains to answer a VERY, VERY simple questions - "What does X% represent... ", my reasons are precisely because I'm trying to decompose best practices!

Which get's into why I'm asking this question at all...

1) I AM a newbie to reef keeping

2) I am NOT a newbie to detail, planned, hard core, highly accomplished hobbyist aquatics

3) In preparation for my first reef tank, I have been undertaking a systematic (far beyond information available at ReefCentral) study of apparently successful large SPS (or mixed SPS dominant) reef tanks.

4) Some of the data seems to point to some easily substantiated "best practices" for the type of tank (softies vs. LPS vs. SPS vs. mixed) I'd like to set up.

5) Some "best practices" (like 410-500 ppm Ca as a single example) seem very clear, yet others are illusive.

6) One of the illusive measures is "Water changed per month". Not because I don't know what that measure is for long term, successful, large tanks is (it's 15-20% or more per month). It's because I can't find out what that percentage is actually measuring!


Seems like an easy thing. Yet the answer is proving illusive. Though it is beginning to appear as I suspected... Newbies use X as a percentage of their total tank volume, while the cognoscenti use X as a percentage of their total system capacity. And some (very limited few) have the foresight to quote X as a percentage of their nominal (capacity minus volume taken up by illiquid content) total system capacity.

And if that's the case, unlike easy things like Ca PPM, I'm going to have to put some assumptions around my assessment of water change percentages of successful large SPS tanks.

I didn't really want to stray into the "why is he asking this question"... but it seemed like going there was inevitable. Hopefully now you know why I'm asking.


Thanks for the help.

[dots]

Originally posted by scolley

I'm trying to decompose best practices!


4) Some of the data seems to point to some easily substantiated "best practices" for the type of tank (softies vs. LPS vs. SPS vs. mixed) I'd like to set up.

5) Some "best practices" (like 410-500 ppm Ca as a single example) seem very clear, yet others are illusive.


Seems like an easy thing. Yet the answer is proving illusive.

Ding, Ding, Ding, Ding......Bingo, Yahtzee, Light Bulb and all of that.....

Direct questions get direct answers..........

You are either going to be really excited with what I tell you next....or starting to reconsider what you are getting into.....

There are VERY few things in life that are still a mystery it seems, we are still trying to figure this whole reefing thing out.....this is why there are some things that we are fairly sure on, other things we kinda know, and other things we still are working on.

After a while you will see some be modified or thrown out completly.....BTW how many Watts per Gallon do you have lighting your tank?

This is why SPS is so fun, IMO there are still some mysterys to be figured out.......but considering in the early 1990's very few could keep SPS and not near the colorations that we have know says how far we have come.

Unfortunatly, if your the type that wants 1+1=2 all of the time....you may be frustrated to find that results vary and opinions vary on how to get the "best" results.

This is why you share your experiences here, to add to that collective knowlege.

There are a lot of do's and don'ts.....most are to protect you from wasting money or causing unneeded loss of livestock.

In the end, nothing is set in stone and there is more than one way to skin a cat when it comes to "success".......taking the advice of those whom have been where you are and that can save you a ton of grief is a good place to start......but find what works for you........in the end, I am more philisophical about the whole thing and realize success comes from consitency and diligence over time..........which is what I was saying earlier, your coral isn't going to grow because you changed 20% versus 40%, its because your doing it in the first place.........

As you learn, you will see when your tank needs something or is starting to go south.....that is when you change your methods.

Sorry, but there is no true "cookbook recipe".....which is why I like it.

[scolley]

Originally posted by dots Sorry, but there is no true "cookbook recipe".....which is why I like it. [/B]

Thanks for the advice. But you don't have to spend much time lurking here to learn that. It is pretty obvious. Fortunately I'm pretty comfortable with that. Learning and figuring stuff is a large part of the fun.

But there's different ways of learning, and most involved experiential trial and error as you suggest. Yet all experience begins with a starting point. In this case it's my first reef, and my first maintenance regimen. And there's a continuum of possible ways to start.

At one end of the spectrum is the person that is "winging it". Starting with at tank of saltwater and starts adding stuff with little prior knowledge and research. There's LOTS of trial and error guaranteed in that person's path.

On the other end of the spectrum is someone who does not move until they have enough knowledge to be successful right out of the gate - or at least as successful as anyone with zero actual reef keeping experience can be. That's me. Or at least that's the path I've chosen.

And some things are clear before putting a drop of water in a tank. For example, that I would consider an overflow unacceptably noisy. So I bought an overflow large enough to house a Hofer Gurgle Buster (fun building that!). Whether or not that will quiet it enough will have to wait for water in the tank. In that particular area (and many more) I've gone as far as I can go without getting some real experience.

In my particular case, I do not have enough room for a big Rubbermaid trash can, nor room for a mixing station. Not near the DT, not in a room above, below, or beside. It ain't gonna happen. So I am currently planning a 3-part patch mixing setup that will automate multiple, small w/c's every day, with a need for human intervention every 5 - 10 days. If I had more room, I could take a more conventional path, and only be mixing water every month or so. But I don't have that room.

So for me, room is limited. And the smaller the w/c necessary (as in X% changed per month), the smaller the containers I have to use for my batch mixing. And I'm planning the whole thing now, and the size of the containers is a critical factor. Thus the size of the water change is a critical design variable. And I've determined that for a large SPS tank 15-20% "can" be sufficient - and often is. But the question of 15-20% of WHAT? still remains.

Why do all my threads end up as philosophical discussions?

[acrouse]

Why do all my threads end up as philosophical discussions? [/B][/QUOTE]

Near as I can tell, it's because experienced people are explaining-answering your question and you are trying to be too technical since you have not experienced what they are referring to. You seem to be looking for a discussion not an answer. We are just trying to help you, since you said you are a newbie with no experience.

I think you are doing an excellent job in trying to gain knowledge, do all your planning, researching in advance, but until you actually experience your own tank, some aspects of saltwater can't be planned out to a tee. (such as the amount of water you need). Yes-you can try to get close on X% to do your setup-but right down to specific quarts or gallons is not reasonable before your tank is even set up-too many variables.

Because in all reality, the answer to X% really means what amount of water change it takes for YOU to take care of YOUR setup. Which will not be determined until YOU have YOUR tank. And then that X% will still vary.

I understand that your room/space is limited, however you need to plan for the unexpected or you will be greatly disappointed. If you determine that YOUR X for good husbandry is 10gallons a week. Great. But what happens if something happens and your ammonia, nitrates, or nitrites spike and you need to lower fast so not to kill off your tank-now you need to do a 20gallon change-or maybe a 20gallon change 2-3 days in a row??? Or your heater goes on the brink and heats up your tank, you need extra water changes to lower temps-or a fish or coral dies and pollutes the tank-which requires larger water changes to correct??? You overfeed and your biological filtration can't keep up?? Which has now increased your X% that you did not set your system up for???? Not everything is Saltwater can be planned for, things happen unexpectedly.

Alot of problems in saltwater can be helped or corrected with water changes. So you will figure out what X% is when your tank has been running for a while. Some of the greatest planned tanks still have problems!!

good luck
jolene

[Aquarist007]

Originally posted by acrouse
Why do all my threads end up as philosophical discussions?

Near as I can tell, it's because experienced people are explaining-answering your question and you are trying to be too technical since you have not experienced what they are referring to. You seem to be looking for a discussion not an answer. We are just trying to help you, since you said you are a newbie with no experience.

I think you are doing an excellent job in trying to gain knowledge, do all your planning, researching in advance, but until you actually experience your own tank, some aspects of saltwater can't be planned out to a tee. (such as the amount of water you need). Yes-you can try to get close on X% to do your setup-but right down to specific quarts or gallons is not reasonable before your tank is even set up-too many variables.

Because in all reality, the answer to X% really means what amount of water change it takes for YOU to take care of YOUR setup. Which will not be determined until YOU have YOUR tank. And then that X% will still vary.

I understand that your room/space is limited, however you need to plan for the unexpected or you will be greatly disappointed. If you determine that YOUR X for good husbandry is 10gallons a week. Great. But what happens if something happens and your ammonia, nitrates, or nitrites spike and you need to lower fast so not to kill off your tank-now you need to do a 20gallon change-or maybe a 20gallon change 2-3 days in a row??? Or your heater goes on the brink and heats up your tank, you need extra water changes to lower temps-or a fish or coral dies and pollutes the tank-which requires larger water changes to correct??? You overfeed and your biological filtration can't keep up?? Which has now increased your X% that you did not set your system up for???? Not everything is Saltwater can be planned for, things happen unexpectedly.

Alot of problems in saltwater can be helped or corrected with water changes. So you will figure out what X% is when your tank has been running for a while. Some of the greatest planned tanks still have problems!!

good luck
jolene [/B][/QUOTE]

I agree completely Jolene---good answer

[scolley]

Now I'm being told how X% might be different for me. Or that I've got to be prepared for emergencies. I don't think I've asked for any of that information... I don't care right now what X% might be for me. I'll find that out later.

Right now I'm just trying to find an answer to an amazingly simple question about other people's tanks, and what THEY are referring to when they discuss an X% water change.

But getting simple answers to this seemingly simple question seems to be eluding many of the well-intentioned trying to assist me.

So, thanks for your help. Really. I know you are trying to help me. But other than the first few posts, I'm not getting simple answers to my really simple question. So I'm though asking about this.

Thanks.

[dudley moray]

i agree with the fizz that's all i'm sayin!

[Aquarist007]

Originally posted by scolley
Now I'm being told how X% might be different for me. Or that I've got to be prepared for emergencies. I don't think I've asked for any of that information... I don't care right now what X% might be for me. I'll find that out later.

Right now I'm just trying to find an answer to an amazingly simple question about other people's tanks, and what THEY are referring to when they discuss an X% water change.

But getting simple answers to this seemingly simple question seems to be eluding many of the well-intentioned trying to assist me.

So, thanks for your help. Really. I know you are trying to help me. But other than the first few posts, I'm not getting simple answers to my really simple question. So I'm though asking about this.

Thanks.

\

Okay Steve as KISS as I can get

x% water change equals 30 gals for me

[scolley]

Originally posted by capn_hylinur
\

Okay Steve as KISS as I can get

x% water change equals 30 gals for me

WOW! I said I was not going to post any more on this. But the good capn's response helped me understand WHY I'm getting some of the responses I'm getting!

PLEASE take a look at my original post. I am NOT asking how much water to change, not for you, not for me, don't wanna know right now.

What I AM asking is when you say "I'm changing "X" percent... " that is X percent of WHAT? X% of your tank volume? X% of the nominal volume of your tank? X% of the total volume of all the the water in your system?

That X is a percentage of SOMETHING. What is that something?

Thanks. Now I'm through.

[eric@tampa]

Too many x's,I have a headache.