# Water Change: How often



## philly7 (Apr 15, 2011)

Hello:

Please advise on when you set up a tank and all live plants and fish are keep running what is the proper way to maintain the system. How often do you have to change water and what is the proper way to do that? Besides checking the nitrites, nitrates, and ammonia what else needs to be done routinely.

Thank you!


----------



## mec102778 (Feb 17, 2011)

Loaded question cause there could be a lot that needs to be done and there could be less than a lot. LOL Sorry but true.

Check th Water Parameters at least once a week, more if you start to see issues good bet to check the water parameters before and after any major changes so you know if you if something is happening in the tank that wasn't planned.
Clean the glass
Change the water as needed or weekly, more frequently if it needs
Dose plant food weekly at least


----------



## rtbob (Jul 18, 2010)

Everyone has their own way of maintaining their own aquariums. Many change 50% of their water once a week using a substrate vacuum. Others opt for a smaller % twice a week vacuuming 1/2 the substrate at each change. There is even one person on this forum who did his first water change in something like two years if my memory serves me correctly. This user is advanced and has a heavily planted tank.

As I have no real plants in my tank to help keep my nitrates in check I base the % and frequency of my water changes on my nitrate levels. Right now 50% changed out every 7-9 days keeps my levels between 35-15ppm.

For my weekly change I take the water directly from the column with no vacuuming. I also rinse my filter media during this maintenance.

Every six weeks I do a complete overhaul of my tanks. I remove all the things inside the tank. Rinse it all under tap water. I then do a thorough, deep vacuuming of the entire substrate. At this time the filters are not touched.

Using the above method works for me. I have yet to trigger a "mini cycle". My nitrates never get to 40ppm.

With a planted tank it might be totally different. I'll leave it to those people with planted tanks to advise you.

It might help if you specify the size of your tank, what filter (s) you are using, type of substrate, current fish in the tank, what and how often you feed the fish. More info from you will allow us to help you even better!

Take care and Good Luck!


----------



## beaslbob (May 29, 2009)

philly7 said:


> Hello:
> 
> Please advise on when you set up a tank and all live plants and fish are keep running what is the proper way to maintain the system. How often do you have to change water and what is the proper way to do that? Besides checking the nitrites, nitrates, and ammonia what else needs to be done routinely.
> 
> Thank you!


With a planted tank you 

1) feed the fish

2) replace water that evaporates.


And that's it.

I have ran tanks for up to 9 years with no water changes and with descendants of the original cycle fish.

I have ran a mixed reef tank for 5 years with no water changes. But the reef system does require dosing to keep calcium /alk/magnesium at correct levels.

my .02


----------



## mrnmrskyle (Mar 4, 2011)

mine has been running 2 months and has never been changed except to add 2 gallons or so a week from evaporating (i'm assuming everyone has that problem). i have a 55 gallon w/ 21 cichlids, a fidler crab and an albino bristlenose pleco, probably 5 plants (which are not doing to well even after adding the liquid food that just made my glass algae grow). i check my water every other day and it has never had a single problem, but my filtration and aeration system are very good. i will be doing a quick vacumm over probably next week just for kicks and giggles, but my water has always been crystal clear and good parameters


----------



## majerah1 (Oct 29, 2010)

I do waterchanges once a week,about 50%.I don have evap issues because I have a glass canopy and the whole top is basically sealed.This is a planted tank,and the reason i do so much is EI fert dosing.


----------



## phys (Feb 4, 2011)

Take what you hear from these posters and figure out what works for your aquarium. Best thing to do is to not do a water change for a few days and watch the nitrates. If they begin to get higher and higher, then you dont have the proper planting to get them out of the water. So when you see the nitrates start to rise above 40ppm, then you should do a 50% water change. When you see them start to rise above 20, do a 50% water change. And when they start to rise above 10, do a 25% water change and keep doing them to keep them around 10 or below. That will help you figure out what kind of schedule you need for water changes. You can also help that out by feeding less and adding plants to your tank. Plants will help scrub the nitrates from the water and increase the amount of time between water changes.


----------



## PolymerTim (Sep 22, 2009)

^ +1

Pretty much what phys said, except that I would point out that if you do a 50% water change when nitrates are 40, then they will be 20 as soon as your done 

Basically, my theory is that the water chemistry will tell you most of what you need to know. If your tank is properly cycled and not overloaded, you should never see measurable ammonia or nitrites. Nitrates will depend on how many fish you have in the tank, your feeding schedule, and your live plants. You should find out what level of nitrates are safe for your fish. Some fish are more sensitive than others. In my case, I have pretty sturdy fish, so I keep my nitrates between 20-40ppm with 35% water changes every 3 weeks. If you have more sensitive fish, you will probably wan to keep the nitrates below 10 ppm.

In general, larger water changes will be more effective at removing nitrates than more frequent smaller ones (do the math), but it is not generally recommended to change out more than 50% of your water at once since this can stress the fish. The smaller the water change, the less shock to the fish.

As far as any other maintenance, I think this covers the most important parts. Most common mistakes can be prevented by understanding the nitrogen cycle:
The Aquarium Nitrogen Cycle
From it you learn why you should not over feed, not put too many fish in one aquarium, not add too many fish at once, clean your gravel or have sufficient plant growth, and do partial water changes.

If you haven't started your aquarium yet, then of course there's plenty of homework you can do on what kind of fish you want, which ones get along together, what kind of water parameters they prefer, what kind of water parameters you already have without trying to adjust them (not generally recommended), common fish ailments, etc.


----------



## jrman83 (Jul 9, 2010)

I would just say change 25% per week and make it happen without fail and it becomes practice. If you plan for it every week you run less risk of things happening where you are now way behind and now having issues. If you're new to fishkeeping, then this is even more necessary...making it a "normal" practice. Test afterwards and see if you need to increase % and go from there.


----------



## Scuff (Aug 10, 2010)

PolymerTim said:


> I would point out that if you do a 50% water change when nitrates are 40, then they will be 20 as soon as your done


Actually, interestingly enough, it doesn't work this way, which struck me as rather odd. It's called Residuals, and calculating it out can be a bit mathy (but thankfully not really necessary to do unless you're a nerd like me). Here's a link to a great description of it:

Math for water changes in the home aquarium - General

Jump down to Concepts of Dilutions and Residuals. I'm not expecting the OP to go and learn this stuff, but I figured I'd share this interesting little tidbit of info with the rest of you.


----------



## philly7 (Apr 15, 2011)

beaslbob said:


> With a planted tank you
> 
> 1) feed the fish
> 
> ...



Thank you! When you replace water that evaporates you just add tap water? or what the proper procedure of adding water?


----------



## Scuff (Aug 10, 2010)

You can add tap water as long as you use a water conditioner as well (assuming your tap water is horrid sewage).


----------



## beaslbob (May 29, 2009)

philly7 said:


> Thank you! When you replace water that evaporates you just add tap water? or what the proper procedure of adding water?


I just run cold water for a minute then fill up a jar. And add that to the tank. With very small amounts temperature, chorine and so on are not a problem.

On the math of water changes.

consider the replacement water is constant, the tank starts at some initial value, and the value is changing at a constant rate each day. (could be nitrates or anything else that is a linear measure.)

After sufficient water changes to where the values just before the water change is constant water change to water change,  What is the value just before the water change?

Ans

just before water change=value in replacement water+(value increase between water changes)/(fraction of water change)


example 10% water change:

value=replacement water+(value change)/1/10
=replacement water+10 times (value change)

value goes down to 9 times after water change then back up to 10 times before the next

5% (1/20)

replacement water +20 times(value change)

back down to 19 times then back up to 20 before next


20% (1/5) 5 times
33% 3 times

This is why I emphasize balancing out the tank with plants. If the plants fully consume nitrates then nitrates will be 0 at all times regardless of the water changes accomplished.


my .02


----------



## Scuff (Aug 10, 2010)

I just did a big, happy nerd sigh, Beasl. <3


----------



## jrman83 (Jul 9, 2010)

And to think I'll never get that part of my life back....reading over that formula.


----------



## snail (Aug 6, 2010)

jrman83 said:


> I would just say change 25% per week and make it happen without fail and it becomes practice. If you plan for it every week you run less risk of things happening where you are now way behind and now having issues. If you're new to fishkeeping, then this is even more necessary...making it a "normal" practice. Test afterwards and see if you need to increase % and go from there.


I'd say this is the standard approach and therefore safest and most straightforward for the beginner as most advice and information you will read is based on this. In practice most fish keepers don't stick to that as they have worked out what works for them. Some have had great success with no water changes but if you go that way there are pitfalls and it only works with well planted tanks.


----------



## 8878 (Apr 15, 2011)

I do 10% every other day. They key is staying uniform, in time and amount. As I have discovered, if you get behind and try to make up for it you are practically giving your fish a death sentence. Fish like routines.


----------



## snail (Aug 6, 2010)

I'm a bit haphazard but I have very low stocking levels and planted tanks.


----------



## beaslbob (May 29, 2009)

Scuff said:


> I just did a big, happy nerd sigh, Beasl. <3


gee is that :

1) because I was done

or

2) you actaully understood it. 


*r2


ya'll can now have your lives back *old dude


----------



## majerah1 (Oct 29, 2010)

Ill ask my daughter to translate all that for me beasl.My head hurts now,haha.


----------



## saltydad (Jun 27, 2008)

I change 40% every two weeks, If parameters call for it, more frequently. I have a 20 long planted FW tank. With salt, I do about 30% a week for reef tanks.


----------



## PolymerTim (Sep 22, 2009)

Scuff said:


> Actually, interestingly enough, it doesn't work this way, which struck me as rather odd. It's called Residuals, and calculating it out can be a bit mathy (but thankfully not really necessary to do unless you're a nerd like me). Here's a link to a great description of it:
> 
> Math for water changes in the home aquarium - General
> 
> Jump down to Concepts of Dilutions and Residuals. I'm not expecting the OP to go and learn this stuff, but I figured I'd share this interesting little tidbit of info with the rest of you.


I'm a bit of a nerd myself, so I'll dive right in  That's an interesting link, but you might want to review it since it confirms my original point. If you have a starting value of 40 and you do a 50% water change, the value should be 20 immediately after the water change. Notice in his first table that, with 50% water changes, a starting value of 100 becomes 50 and a starting value of 50 becomes 25? Nothing unexpected here. The point he is stressing in this article, is how many water changes of a given percentage you have to do before you have removed most of the old water (and with it the contaminants). The common misconception here is that (for example) two 15% water changes are not the same as one 30% water change. It's pretty clear when you do the math, but not always obvious until you think about it carefully.

The author does admit though that he ignores the build up of fresh contaminants. While this would complicate the math slightly, I think it is critical to aquarium water change math because, in the end, it doesn't matter how old the water is or how much old water you have versus new water. What matters are primarily a) what are the pollutant concentrations and b) what is the magnitude of change experienced by your fish during the water change.





beaslbob said:


> consider the replacement water is constant, the tank starts at some initial value, and the value is changing at a constant rate each day...
> 
> After sufficient water changes to where the values just before the water change is constant water change to water change, What is the value just before the water change? ...
> 
> ...


Well, I have to admit, I've spent far too much time trying to figure out what you're saying here, and somehow I'm missing it. I get your conclusion that, for example, if you are doing 10% water changes, then the value across any given water change will decrease by 10%, but I think you're trying to say something more than that.

I'm going to take my own stab at the math and see if that is helpful to anyone.

First a few definitions of my own choosing to make the equations a bit more clear to see:
- Ch = concentration high = the value just before your water change or the max that you want to allow in your aquarium of a given reading like nitrates
- Cl = concentration low = the value just after the water change
- Ct = concetration tap = the value of your tap water (or more appropriately the replacement water after adding any conditioners, etc.)
- %WC = % water change = the volume of water you replace divided by the volume of water in the tank

Note that this ignores the effect of evaporation, which is minimal for anyone doing regular water changes.

If you know the value for your replacement water, your tank water, and the amount of water you're going to change then the value after the change will be:
*Cl = Ch * (1 - %WC) + Ct * %WC*
This is simply a weighted average of the old tank water and the new replacement water.

Now if you're trying to set up some kind of a routine, what might be more useful is an answer to a question like:
"If I want to do 15% water changes, how often do I have to do them to keep my nitrates below 20 ppm?"

For this, we only need one additional piece of information which is the rate of increase of the measured value. For this calculation, I will call it:
- dCd = delta concentration daily = change in concentration each day

To get this number you may want to measure over a longer period such as 1-2 weeks and divide by the number of days. This numer won't be very accurate based on a typical liquid test kit result, but should at least get you a ball park estimate. Another caveat is that this rate may not always be the same in your tank. It will of course depend on many factors including frequency of gravel cleaning, which many of us do during the partial water change. With that said, I think this will still be a good first approximation:

freq = frequency of water changes in days
*freq = (Ch - Cl) / dCd*

In this case, you will have to calculate dCd from your own measurements as mentioned above; Ch is a max level of your own choosing, and Cl comes from the previous calculation. If we substitute in the equation from before for Cl and do a little rearranging, we get a fairly simple, although not intuitive equation:

*freq = %WC * (Ch - Ct) / dCd*

Likewise, if you determined that you were willing to do water changes once per week and wanted to know how big a water change you would have to do to keep the levels below Ch, you would simply rearrange this equation to:

*%WC = freq * dCd / (Ch - Ct)*


Now that I've scratched my math itch, I have to admit that most people aren't willing to plug numbers into even these simple equations if given them. Also, the bioload, feeding schedules, and cleaning routines vary so much between tanks that I believe it is overly simplistic to quote a standard water change routine for all tanks. My recommendation for anyone new to the hobby is to get a liquid test kit, start with a typical water change plan that is consistent, and adjust the freq and/or %WC to achieve the levels reasonable for the fish they keep. The balance here will be to have a frequency low enough to keep your sanity and also a %WC low enough to have minimal shock to the fish during the water change.

It is much better to measure than to calculate the theoretical. 
It is much better to calculate the theoretical than to guess by rules of thumb. 
It is much better to guess by rules of thumb than to be totally unaware of the nitrogen cycle.



Hope this helps somebody. I had fun typing it


----------



## phys (Feb 4, 2011)

I like this polymertim person.. he speaks my brain language... thanks for putting my thoughts into words, i'm not good at the whole word part. You really put down everything i would have if i'd been able to make my thoughts go through my fingers. Hopefully this will help some people! I'm sure it will.


----------



## jrman83 (Jul 9, 2010)

I'm sure....

One way or the other way too far left for the guy asking the question. It was a simple question that has a simple answer and that ain't it. Too much for me to even want to read.


----------



## rtbob (Jul 18, 2010)

I take the easy way out. nitrates pre water change = 40. Replace 50% of the tank water with tap water which has a nitrate level of 0. 40-50%=20. No matter what.

Unless you have nitrate peeing invisible trolls in your house! That changes everything.


----------



## jrman83 (Jul 9, 2010)

rtbob said:


> Unless you have nitrate peeing invisible trolls in your house! That changes everything.


*r2 That would definitely raise a concern.


----------



## Scuff (Aug 10, 2010)

rtbob said:


> Unless you have nitrate peeing invisible trolls in your house! That changes everything.


You mean you guys don't...? Uh...brb...


----------



## Scuff (Aug 10, 2010)

Anyone know the number of a good exterminator, btw...?

_Totally unrelated.

_>_>
<_<


----------



## beaslbob (May 29, 2009)

majerah1 said:


> Ill ask my daughter to translate all that for me beasl.My head hurts now,haha.


and pm/email is available for your daughter also. *old dude*r2

my .02


----------



## holly12 (Apr 21, 2011)

I have a 10g freshwater community, amphibian and invertebrate tank. I do a 25% water change every week, (vacuuming the gravel each time). About once a month while doing the water change/vacuuming, I pick up the decorations to vacuum the gravel underneath them.

After the water change, I put in the recommended dose of water conditioner/stress coat (I'm on a well, so the conditioner acts more as a stress coat rather than a conditioner), and the recommended dose of "Cycle".

I have some live plants, so once I've changed the water, I add in the recommended dose of plant fertilizer.

I rinse the filter mediums in the dirty fish water each week, (replacing the mediums as needed - carbon = once a month, sponge = once every 3 months, bio-max = once every 3 months). I take the filter out and give it a clean/wipe/rinse with tap water once a month. (Never change all the filter media at the same time, and try not to clean the whole filter on the same week as you change any of the media).

I don't scrape any algae off of the glass or decor because I let my pleco (and soon to be Zebra Snails) eat it. They do a pretty good job!

As for the lid of the tank, every once in a while the lid needs a wipe down to get rid of any old food flakes that are caught on it - sometimes the food can start to grow mold on it - and the glass on the lid gets a wipe down so that the light can get in properly.

Hope this helps some.


----------



## snail (Aug 6, 2010)

holly12, nice description of basic tank maintenance.


----------



## holly12 (Apr 21, 2011)

Thanks Snail! *thanks I know that some people do a lot more when cleaning their tanks and some do a lot less - this is just what seems to work best for my tank.


----------



## phys (Feb 4, 2011)

Exactly holly12! The best thing to do is follow advice as a guideline and figure out what works best. Not everyone has exactly the same tank so things will be different.


----------



## holly12 (Apr 21, 2011)

Thanks Phys! *thanks I've spent a lot of time asking LFS people, friends, searching the internet, for answers on the "how to's" of tank care. Of course this forum is always a great resource for many tank issues, I've come to learn that a lot of the time, I've just got to figure out what works best for me and my tank.


----------



## beaslbob (May 29, 2009)

Gee shouldn'd all those %'s be fractions? not 10 but .1 for instance?


Now for your homework should you choose to accept it.

given that a "thing" is increasing a 1/day (ppm or whatever).

given you are following some water change schedule that is "timed" to the amount of water change such that you change 1%/day. Like 10% every 10 days, 33% every 33 days. 20% every 20 days?

And you have some value in the replacement water.

and some initial condition in the tank.

What is the value of that "thing" before a water change?


Now time for me to take a break and the jepordy music plays.

*pc

my .02








PolymerTim said:


> I'm a bit of a nerd myself, so I'll dive right in  That's an interesting link, but you might want to review it since it confirms my original point. If you have a starting value of 40 and you do a 50% water change, the value should be 20 immediately after the water change. Notice in his first table that, with 50% water changes, a starting value of 100 becomes 50 and a starting value of 50 becomes 25? Nothing unexpected here. The point he is stressing in this article, is how many water changes of a given percentage you have to do before you have removed most of the old water (and with it the contaminants). The common misconception here is that (for example) two 15% water changes are not the same as one 30% water change. It's pretty clear when you do the math, but not always obvious until you think about it carefully.
> 
> The author does admit though that he ignores the build up of fresh contaminants. While this would complicate the math slightly, I think it is critical to aquarium water change math because, in the end, it doesn't matter how old the water is or how much old water you have versus new water. What matters are primarily a) what are the pollutant concentrations and b) what is the magnitude of change experienced by your fish during the water change.
> 
> ...


----------



## PolymerTim (Sep 22, 2009)

jrman83 said:


> I'm sure....
> 
> One way or the other way too far left for the guy asking the question. It was a simple question that has a simple answer and that ain't it. Too much for me to even want to read.


jrman,

You're correct. To be honest, I wasn't trying to answer the OP's question so much as having a little fun with the math as an aside. My general advice for the OP is located in the last paragraph, which in retrospect I should have placed at the top  I think Holly did a great job with an example of a good starting point for general maintenance.





beaslbob said:


> Gee shouldn'd all those %'s be fractions? not 10 but .1 for instance?
> 
> 
> Now for your homework should you choose to accept it.
> ...


Yes, you're right that the %'s should be input as fractions. I apologize if that confused anyone. So 10% would be put in as 0.1 or 10%, not 10. I tried to clarify that in my definition, but it may have been misleading.

As for the homework assignment, it was pretty fun. I'm sure there is a way to derive the relationship from first principles, but I'm not that much of a math wiz, so I set up some spreadsheet tables based on the equations I gave and ran them for enough iterations to come to a steady state where the concentration before the water change is always the same. Then I played around with the inputs and determined a functioning relationship empirically. Here's what I came up with:

Where:
Ct = concentration tap = concentration in replacement water
WC = fractional water change
dCd = change in aquarium value daily
Days = days between water changes (or inverse of freq)
Ceq = equilibrium concentration before water change

Ceq = Days / WC * dCd + Ct

As a note, the starting value in the tank has no effect on this equilibrium concentration since it is diluted over time. So, going back to your question, if we set dCd equal to 1 unit/day, and you "timed" your water changes such that Days / WC = 100 (e.g. 10 days / 10% = 100), then the equation reduces to:

Ceq = 100 + Ct

Interestingly, the equation seems to work well for my aquarium. I've been running for over a year now and performing a 35% PWC every 2 weeks gets me about 40 ppm nitrates both by the equation and in real life. 

So now I think I get your earlier post (thanks for leading me to the interpretation). Your relationship was:

equilibrium value = replacement water + value increase between water changes / fraction of water change

In this case, the value increase between water changes is represented in my terms by Days * dCd. So rearranging a bit: Ceq = (Days * dCd) / WC + Ct ...they are the same!

Thanks againfor the clarification. Now I can sleep more soundly at night


----------



## Zookeeper (Apr 27, 2011)

For a new tank, not cycled, I do 50% WC every other day with one half gravel vacc a week for non planted and every 3 days for planted.

For an established tank without plants I do 20% every 3 days. Planted tank, 10% a week

You can keep them with the same water but they suffer old tank syndrome (mass deaths) when you add fresh clean water eventually. Odd thought but so true. 

Other than that, swish your filter in used tank water every change, never use tap water unless you are running a chlorine free well. I personally dump the carbon out after a month and use the filter until it's falling apart or to clogged to work to avoid a mini cycle. I wipe the inside of my tanks with an aquarium safe sponge once a month but I have snails in my non planted to clean up and my planted tank is never dirty. 

I don't use ferts, very low tech, and my plants are fine. If you choose to go this method you must research your plants and the bioload of your fish to make sure it evens out . 

I know you didn't ask but ghost shrimp are amazing in a planted tank. I attribute the crystal clear tank to them. Awesome little cleaners and 0.30 cents each!


----------



## beaslbob (May 29, 2009)

PolymerTim said:


> ....
> 
> Ceq = 100 + Ct
> 
> ...


That is correct!

The final equilibrium value before any of the water changes will be 100 times the daily change plus whatever is in the replacement water.


As a review the problem specified water changes that were 1%/day ( or multiples) with a constant daily change in tank conditions.

Now let's step back and consider.

100% water change every 100 days
50% every 50 days
10% every 10 days
1% per day
constant water change at the rate of 1% per day.


all result in 100 times the daily change plus replacement water before the water changes.

It is not uncommon to have a 1ppm/day change in nitrates so that means 100ppm nitrates.

Under those conditions you would have to do water changes equal to 10%/day to limit nitrates to 10ppm. of 100% per day to limit nitrates to 1ppm.

Yet I have had tanks both fw and marine that have 0 nitrates and phosphates (nitrates api, phosphates salifert) for years with no water changes.

The reason is I use plant life (fw plants, marine macro algaes) to consume the nitrates and phospahtes as they are being gnerated.

So to me the lesson is to set up the tank right from the beginning balanced out with plant life and just leave it basically alone. Sometimes I get cloudiness and cyano but kill the lights to rebalance out the nitrates and phosphates then resume with less lighting and feeding to maintain the balance.

All is not totally hands off as I do have to dose calcium/alk/magnesium in the reef tanks.

But I am absolutely sure that water changes at any reasonable level in our closed systems do not maintain much but rather mask underlying problems.

The important thing is to balance out the tank so water changes are irrelvant.

may .02


----------

