# Largest water change



## kilicar (Nov 3, 2006)

what is the largest water change one can do to a tank using not filtered water? (% wise)


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## Dawgz (Aug 18, 2005)

well the question isnt really answerable...depends on the situation...

regular water changes are like 30-35%

u can safely do 50-60% sometimes if something's up in ur tank...

i think, a 75 would be the MAX i would recommend...ur fish will be super stressed tho.

but ive heard stories of noobs doing 100% changes with no ill effects, just some super stressed out fish...

noobs =\


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## Leasure1 (Jul 24, 2006)

Agree with dawgz....up to 75%


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## kilicar (Nov 3, 2006)

Dawgz said:


> well the question isnt really answerable...depends on the situation...
> 
> regular water changes are like 30-35%
> 
> ...


lol, the most I ever did was 50 just wondering how bad it was for them


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## AJerman (Nov 7, 2007)

Yeah, I personally wouldn't go over 50% unless there's an emergency. I let a tank get out of hand one time and my nitrate was pretty high, but rather than changing a large amount all at once I did about a 30% change 2 days in a row. I feel that even that 1 day gap gives the fish a little more time to be aclimated. Even then I noticed a little bit of flashing from it.


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## Dr. Giggles (Oct 18, 2003)

I have to disagree on some of these reply's, only because if a pH reading in a tank is lets say for shits and giggles 6.6 and you change out 75% of the water with tap water of lets say 7.5 or higher and threw the fish in. The end result will be a dead fish. However, not mentioned in this topic, If the pH is significantly different and you put your fish in a cooler of tank water and then took out 75% or 100% than you slowly added the new tank water to the cooler to a 50-50 mix than your fish would be properly acclimated to the new tank water and that would be fine. So the bottom line is you need to know the pH in the tank and the pH of the water you will be putting back in. If they are similar than it don't matter on the size of the change, otherwise the difference will dictate how safe your big water changes would be. You could never go wrong with a 25-30% change imo. A 50% could cause stress but in an emergency it could be done.


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## Grosse Gurke (Jan 3, 2003)

I think tank size has something to do with this as well. I used to do 50% changes on my 180 gallon tanks all the time with no issue because when filling the tank up.....it takes a while and is almost like an acclimation process. But if you do a 50% on a 10 gallon the tank fills up very quickly and can shock the fish. I think the volume of water is critical to your water change regiment....


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## Piranha_man (Jan 29, 2005)

I've always considered 50% to be the ceiling.
I usually change all mine weekly at between 40%-45%.

It's amazing to me how many people out there have aquariums and know nothing about cycling.
I find people all the time at the pet store and such telling of how every few months or so they empty all the water out of the tank, wash the gravel and plastic plants and then refill it and put the fish back in.
Talk about being in a constant state of shock!

This is why there's such a high mortality rate in the _average joe's _tanks.

Thankfully, almost everybody here knows much better than this.


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## pirayaman (Nov 3, 2007)

ive had my ph as low as 5 and then it went to 7 i had no dead piranhas this has happened more than once as well i think these fish are used to quick changes in ph in the wild in dry to wet their must be a flash flood that jacks the ph up like mad may be imn wrong but what may really be killing the fish with a ph flucuation is the ammona as it is more deadly at a higher ph


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## NegativeSpin (Aug 1, 2007)

I came up with a little experiment that can determine the maximum water change in one afternoon. Get a glass or cup that isn't tapered, ideally a graduated cylinder, and fill it half way with your aquarium water and dilute it out with your tap water. Check the pH before and after you do this. If the difference in pH is greater than 0.2 repeat the process with 10% more aquarium water. If the pH difference is less than 0.2 repeat the process with 10% less aquarium water. You can probably get your ideal volume change in less than 10 minutes.


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## Dr. Giggles (Oct 18, 2003)

pirayaman said:


> ive had my ph as low as 5 and then it went to 7 i had no dead piranhas this has happened more than once as well i think these fish are used to quick changes in ph in the wild in dry to wet their must be a flash flood that jacks the ph up like mad may be imn wrong but what may really be killing the fish with a ph flucuation is the ammona as it is more deadly at a higher ph


You're lucky you did not lose the fish, but a pH of 5.0 in an aquarium your bacteria starts dieing off which will explain any ammonia readings you may get and in a properly established filter the ammonia produced by the fish will have no bearing in a higher pH tank because the nitrifying process is instant.


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## notaverage (Sep 10, 2005)

I max at 25% if i let it go for over a week or more which is rare...maybe 30-35%
My tank stays clean though....i dont let ANYTHING sit in the tank longer then 30 min. and constantly spot clean


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## remy5405 (Feb 8, 2008)

With my RB's 2x 6in in a 75gal(about 1.2years old) i change aprox 10% twice a week. i dont filter the water or do anything to it. i just fill 2 5 gal buckets and leave them under the stand for a day. this lets the temp in the buckets to become room temp and also lets any chlorien evaporate off. i figure if my take is 80* and the bucket water is 70* and its only 10% (7gal is 10% of take plus any top off water) then the temp swing is only maybe 1*.
On a side note... I have had my salt tank (150gal) going for over 4 years with never changing the water, only topping off with kalk and/or buffer.
I also feel that if you are getting ph swings then you need some freshwater buffer in there.
But to answer your question, i wont do more then 33%=1/3 at a time. if more is needed then do it twice a day atleast 4hr apart.


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