Partial water changes/how often?

[Steve_B]

Hey guys, I'm here because I have a fish only, strictly not a reef system. I'm starting a community tank that I'm in the process of stocking up now.
I've always had large aggressive tanks
and after 20 years of it I'm done. :wavehand:

I realize that this isn't a question that everybody can answer in the same way because of many other factors.

I pretty much go by where my nitrate levels are. When it gets to about 20PPM, I make a change, in many cases higher than 30ppm. I've been doing this for years with my big guys and it has always worked well for me.

I was advised to make a 25% change weekly.
That 25% per week seems WAY unnecessary to me. I've never done more than monthly water changes of maybe 25%

Come on, at 25% per week you have basically replaced all of the water in a month. I'm obviously good at counting on my fingers.:lmao:

How do you guys figure out when and how much water to change?

 

[MrTuskfish]

I stock fairly heavily and have done about 20% monthly for years. I don't worry about nitrate in FOWLRs as long as they don't get much above 60ppm. I'm not saying don't do anything about nitrate; but I've never seen any real study that says they bother fish at any level. However, I thnk nitrate at, say 80+ppm, indicates a general lack of housekeeping. WCs also do a lot more than just control nitrate; they eliminate some organics and other potential toxins and replace other minor salt ingredients that have become exhausted.

 

[Recty]

It's seems a little counter intuitive to some, but I'll try to explain my thoughts on it.

For theory's sake, lets say that your levels increase by 10ppm nitrates per week.

Lets say in a 100g tank, you have 100ppm nitrates. You replace 20% of the water with clean, freshly mixed, 0 nitrate water. You've diluted the nitrates by 20%. 80ppm nitrates now...

In a week, you've got 90ppm nitrates. Do another 20% water change. Now your nitrates are 72ppm.

In a week, you've got 82ppm nitrates. Another 20% water change, now you're at 66ppm.

In a week, you're at 76ppm nitrates. Do your forth water change and you're at 61ppm nitrates.

So over the course of 4 water changes and 80% of your tanks total volume you've actually only lower your ppm by 40ppm. And by the end of the last week after the last water change, you're back over 70ppm nitrates. Every water change you do gives you diminishing returns because you're replacing part of the water you already replaced last week. If you could somehow magically keep the clean water separate from the dirty water and replace only 20g weekly of dirty, then yes, in 4 weeks and five water changes you'd have all new water, but that's not the way it works since water mixes.

NOW, let's go with the way I like to do water changes, keep in mind this is with FOWLR, not reef. I'm not sure I would do this with any delicate inverts in the tank.

100g tank, 100ppm nitrates. Drain 80g of water out. Now you've got 20g total water volume left, at 100ppm nitrates.

Add 80g of new water. Guess what? Your nitrates are now 20ppm. Over the course of 4 weeks, your ppm will creep up to 60ppm. Practically the same as the other method, except the average PPM of nitrates and other waste products that the fish have been in for that entire month is 40ppm AVERAGE.

In the first method, fish were exposed over the month to a 76ppm nitrates average...

Anyway, numbers can vary and depending on how you feed and your filtration method, you can accumulate more or less nitrates over a week than a steady 10ppm increase.

The end result? Doing a LARGE water change and then going longer between them keeps the water cleaner on average, and arguably a LOT cleaner. Think of it this way, you're living in a city with high smog levels... would you rather the administration clean the air in small amounts once a week and keep you breathing harmful gases at only a slightly diluted level? Or do a big monthly cleaning that almost eliminates gases and then slowly lets them creep up over time? At the end of the month you're going to have the same amount of harmful gases in the air again, but you'll have breathed a LOT less harmful gas total with the second method and be healthier.

ALSO, it's so much easier on the person doing the water change. Get your water mixing a week before you plan on doing it, allow the pH to balance, throw in a heater the last day or two, and just get ready to do a big change. This doesnt require weekly mixing of water... just a once a month thing.

The downside is if you arent good at water changes and screw it up, you're dumping in a lot of water and if the pH is horrible or the salinity is way off, you're affecting your water in a major way whereas if you only replaced 20%, it's not such a major event for the fish.

Anyway, when I started keeping large, hungry, aggressive fish in my old 210, after I came out of hypo the last time I started doing LARGE water changes, like to the tune of 140-150 gallons once every 2 months. My water never looked better and my fish thrived.

To each his own, this method is not for everyone, but I think your overall water quality and therefore fish health is better when you do large infrequent water changes.

The other method Danorth used to do which was a little too extreme to me is do an 80% water change. So in this example 20g of water left, 100ppm nitrates. Add clean saltwater to the tank, make sure you double the amount of water you left in it. So in this instance, add 20g more water. You'll have 40g of water with 50ppm nitrates. Drain half of that again, back down to 20g, with 50ppm nitrates. NOW do your 80g refill, and you've got 10ppm total nitrates. You've used only 25% more water and you've cut your nitrates by 50% from the 2nd method. And the more water you remove at first, like say you get down to 10% water left, the more drastic this method decreases your nitrates and other pollutants. Heck, Dan did this method and wouldnt do water changes for 3-4 months.

Anyway, that was a little much for me but he succeeded quite well with it. I'm more of a fan of method #2 though.

 

[reefergeorge]

Recty, While I understand the math behind your theory. I have read a few reports on smaller more frequent WCs being less than a percent different than one large wc. I'm on your side and like doing close to 50%, but I just want the info out there.

I'll try to find it again.

 

[reefergeorge]

Aquarists often think that many small changes are not as efficient as one big change since some of the water in all subsequent changes was already replaced by earlier changes. This is a correct assertion, but it is often overstressed. After changing 10% three times, only 10% of the first 10% change was changed the second time (1% of the total). So the difference is small. We can mathematically calculate the efficiency of such changes as follows. If we use our 30% example, then one 30% change removes 30% of the impurities, assuming an equal distribution of the impurity within the water. If we do six 5% changes, then the reduction in impurities = 1-(0.95)6 = 26.5%. So it is less efficient (six 5% changes exactly equal 26.5% changed in one batch), but it is not radically less efficient. Going smaller still, the difference is even smaller. Doing 30 one percent changes removes 1-(0.99)30 = 26.0% of the impurities.

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

 

[Steve_B]

I didn't have 6 hours to read and calculate all of the #s here, but I think that 25% per month to keep nitrate lower 30ppm isn't needed. I've also spoken to many professionals that think keeping it less than 70 PPM IS FINE IN A FISH ONLY TANK. It's a PITA to even make monthly water changes. Long ago I used to let the nitrate hit 50PPM. It seemed to put no more stress on the fish than making it never go over 30PPM. I do understand the calculations that making all of these small water changes really isn't necessary or even accomplishes anything we are looking for as far as water quality goes. It seems that less frequent larger changes actually make more of a difference than small changes all of the time.

I'll let the fish tell me what they think and go from there. If I can make 75% changes when the nitrate hits 60PPM all the better. All of the prep work and the change are as I said a big pain in the work involved. I think I finally found the real answer to the stupid 25% per week info. It takes me about 2 days for all of the crap involved, making RODI water, making all of the parameters exactly the same with the new and replaced water. Sc***w that, I have confirmed my theory on this stuff. Like I said, let the fish do the talkin.

 

[mattsilvester]

For FOWLR, I have always been governed by when things look like they need a change. This is perhaps not the best way of doing things, but it has worked well for me. I would test occasionally and if I found nitrates to be getting high I would perform a series of 20-30% changes to get them back in line. But this is a bit of a caviler approach and I would not really recommend it.

25% weekly seems excessive to me. 20-30% seems a sensible minimum - 25% twice per month would be very good ..... generally. But it depends on what you're keeping and how heavy the bioload is. Keep in mind also that the purpose of water changes is more than just removing impurities - it is about replenishing minerals too to help maintain stability of pH, ORP, etc. Fish such as powder blue tangs (1st example I can think of) positively glow when kept in nice clean well maintained and stable tanks - and appear somewhat washed out in less well maintained, less stable systems.

Notwithstanding the above, I believe that in a typical tank if one performs enough water changes to keep their nitrates at 20ppm then it is pretty good husbandry. All things considered, if you keep nitrates below 20ppm then by coincidence the pH etc. tends to be stable and within desired parameters also.

So, for example if you measure your nitrates at the start of the month and they are 20ppm..... if you do nothing and by the end of the month your tank is 25ppm..... so your system is accumulating 5ppm per month..... in which case, a monthly 25% change would be appropriate to maintain stability and balance. e.g. 20ppm, 25% change reduces to 15ppm, then 5ppm accumulation for the month you will be back to 20ppm by months end.

If however you have more rapid accumulation, then I would be inclined to perform bi-weekly water changes e.g. monthly accumulation of 10ppm.... so you'd need to do a monthly 33% (start 20ppm, +10ppm = 30ppm, 33% change = back to 20ppm)..... anything more than 33% changes, in my view, stresses both the fish and the biological activity of the tank - so if your monthly nitrate accumulation exceeds 10ppm, then split it.

As with everything in life - the above depends on context; From the OP's question, I have inferred that we are talking about an "angel, tang, and butterfly" type FOWLR, not a "Trigger, grouper, and puffer" type set up. 20ppm would be very hard to maintain in the latter, and is less critical.

 

[Steve_B]

Thanks for all of the info guys. I have a 225 in my garage just trying to dump it for whatever I can get. I've had it with 10" Queen Angles squaring off with big tangs and trying to keep more than 1 trigger and big wrasses and on and on and on. Things went way wrong with leaking bulkheads on the 2nd floor of my house where I had the tank and all of the aggression that I just don't want it anymore. Now I have a 70 gallon ¼ cylinder acrylic tank that is 30" deep down here on my 1st floor. I've started stocking it up now that it has cycled and don't want anything over maybe 4"max fish in this type of tall relatively narrow tank. I want a to have a peaceful community tank that doesn't consist of trying to make large aggressive fishes to live in a tank where their behavior changes as the grow larger and have to change them out with others that wont rip their guts apart. I actually had a relatively small Picasso trigger that was only in the tank for less than one week slam into a tusk that I had just introduced. The trigger hit the Wrasse so hard his scales were ripped off. I never expected a small trigger to make an attack like that. I have had several triggers, another previously that wasn't nearly as aggressive and I guess it's like any other animal. They have a general temperament, but some can be much different than others. I have 2 Persian cats that are like night and day. That's the way of wild; there is no way of knowing one of the same animals being the same as the other.
Give me some little friendly guys that get along that are peaceful and calming, not monsters trying to kill each other all of the time as they mature.

 

[Recty]

Aquarists often think that many small changes are not as efficient as one big change since some of the water in all subsequent changes was already replaced by earlier changes. This is a correct assertion, but it is often overstressed. After changing 10% three times, only 10% of the first 10% change was changed the second time (1% of the total). So the difference is small. We can mathematically calculate the efficiency of such changes as follows. If we use our 30% example, then one 30% change removes 30% of the impurities, assuming an equal distribution of the impurity within the water. If we do six 5% changes, then the reduction in impurities = 1-(0.95)6 = 26.5%. So it is less efficient (six 5% changes exactly equal 26.5% changed in one batch), but it is not radically less efficient. Going smaller still, the difference is even smaller. Doing 30 one percent changes removes 1-(0.99)30 = 26.0% of the impurities.

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

The only thing this doesnt take into account is that the person who does a large water change at the begining of the month has lowered their nitrates by 50% and the fish are in cleaner water for a long time, whereas the person who does it 10% a week is only slowly lowering nitrates and other buildups, providing less clean water on average.

 

[mattsilvester]

The only thing this doesnt take into account is that the person who does a large water change at the begining of the month has lowered their nitrates by 50% and the fish are in cleaner water for a long time, whereas the person who does it 10% a week is only slowly lowering nitrates and other buildups, providing less clean water on average.

But nitrates in themselves are not the true purpose of the water changes; actual nitrate is not that harmful to fish; measuring nitrate is indicative of general water quality and by maintaining nitrate through water changes we maintain good overall waterquality, generally; the term 'water quality' includes parameters suck as salinity, alkalinity, pH, tempeature, and ORP - some of which fish are very sensitive to (as are the biological organisms that comprise the biological filtration of the tank); doing a 50% water change will instantly and rapidly alter all parameters, not just nitrate. This rapid change, albeit for the better, can be very stressful for our fishes and the biological balance of the tank (this is why we take 0.5hr to 1hr to acclimate our new fishes).

Sometimes, wholesale water changes are needed for do-or-die situations; massive die off and huge ammonia spikes, a DSB gone bad, etc. But for routine maintenance it is not recommended.

 

[Recty]

I dont see any harm, at all, in doing a big water change, if you balance the temp, the pH and the salinity. Those seem to be the three major factors that fish care about, in my experience.

In all the time I did large water changes and stopped doing weekly small ones, I never once had an adverse reaction with my fish. However, I took the time to make sure my water was good before adding it.

I had a FOWLR, my rock had little brittle stars and I had some cleaner shrimp in my 210. I never had die off or problems with the delicate inverts.

I do know that nitrates are not the only point of the water change, I've been keeping fish a year or two I could not use the word nitrates, instead just something like pollutants... a large monthly water change takes pollutants out of the water by a 50% volume, and the average cleanliness of the water is significantly higher than the average cleanliness of the water of a tank with small water changes performed weekly.

I dont think a large water change will instantly and rapidly alter ALL parameters, as you so state. If you do it right (this means you dont mix up a 50g drum of water 1 hour before a water change and just dump it in) your parameters should stay solid.

I think it's important to state I'm not just randomly theorizing here, I've done this type of water change for a long time. It works. It's easier on the hobbyist. Arguably, it's healthier for the livestock. At first, when Danorth told me this is how he did his changes, I was skeptical, but it's really a good way to do it.

If you're really worried about the water changing too much, do it in the "drip acclimation" method but apply it to a water change. Take 2 hours and a very small pump and just trickle water back into the tank, then turn your system back online after 2 hours.

Totally unnecessary, imo, but if it made you feel better, great.

Long story short, the average hobbyist probably does better with weekly 10% water changes. Someone with a little experience in the hobby and a spot to mix up a large container of water at once, I think can really benefit from doing monthly water changes.

To each his own, but I'll stick with my method, I've seen nothing but good out of it.

 

[mattsilvester]

..... if you balance the temp, the pH and the salinity. Those seem to be the three major factors that fish care about.......

Recty - respectfully I disagree.

These are the things you can and do regularly measure (test) - there are many other things to test, but do affect your fish.

Have you done much travelling in your life i.e. living in Alaska, does your body feel the stress of going to say Florida or LA. Sure, your room AC keeps the temperature right, but many other factors upset your body system for a day or two as after...... personally, when I travel to say Europe my it plays havoc with my body functions despite the better air quality and food etc. - on the otherhand going to Hongkong, Singapore, Jakarta, Ho Chi Minh, etc. I just feel a little out of sorts because of time differences..... sure, neither will kill me but the small changes are far less stressful and affect things like my blood pressure, colesterol, weight, etc. - over time I feel the difference.

I too have gone through periods where I just did large periodic water changes, brought about by necessity due to personal circumstances. But if one can, it is far better to do bi-monthly 25% changes. One could further argue that bi-weekly water changes keep the water consistently fresher, rather than a once per month "binge of freshness" - LOL.

Stability, and how much it visually benefits our fish, is something that you can really only appreciate over time; it also depends to a large extent on what fish you keep ..... groupers, triggers, etc. are less sensitive than angels and tangs etc.

Each to their own - we'll agree to disagree - I just favour stability in my tank for which I am willing to sacrifice the little bit of additional dilution you get from larger less frequent changes. That being said - if all you can do is a monthly 50% change, you are still doing far more than most that do 20% per month or so......

 

[Recty]

Recty - respectfully I disagree.

These are the things you can and do regularly measure (test) - there are many other things to test, but do affect your fish.

Have you done much travelling in your life i.e. living in Alaska, does your body feel the stress of going to say Florida or LA. Sure, your room AC keeps the temperature right, but many other factors upset your body system for a day or two as after...... personally, when I travel to say Europe my it plays havoc with my body functions despite the better air quality and food etc. - on the otherhand going to Hongkong, Singapore, Jakarta, Ho Chi Minh, etc. I just feel a little out of sorts because of time differences..... sure, neither will kill me but the small changes are far less stressful and affect things like my blood pressure, colesterol, weight, etc. - over time I feel the difference.

I too have gone through periods where I just did large periodic water changes, brought about by necessity due to personal circumstances. But if one can, it is far better to do bi-monthly 25% changes. One could further argue that bi-weekly water changes keep the water consistently fresher, rather than a once per month "binge of freshness" - LOL.

Stability, and how much it visually benefits our fish, is something that you can really only appreciate over time; it also depends to a large extent on what fish you keep ..... groupers, triggers, etc. are less sensitive than angels and tangs etc.

Each to their own - we'll agree to disagree - I just favour stability in my tank for which I am willing to sacrifice the little bit of additional dilution you get from larger less frequent changes. That being said - if all you can do is a monthly 50% change, you are still doing far more than most that do 20% per month or so......

I agree that there are many things besides the three listed that affect your fish, I didnt say that there wasnt. However, I do think those are the three main ones that matter. They are the only three I've ever tested for in my water changes and so far (multiple years of doing this now) I've never had an issue with not measuring phosphates, nitrites, ammonia, alkalinity, calcium, magnesium, strontium... the list goes on and on. And you're correct, if you have delicate fish or inverts, it will be easier to affect your fish poorly with non consistent water when you do your change.

And I do think I stated in my first post on the subject I would only do this on a fish only and not a reef. The chance of having a parameter off in your water change and affecting your entire reef is higher than having a parameter off and your fish caring about it.

In my experience, fish react favorable to clean water over stability. Stability hasnt ever been something I'm worried about, at least not beyond those three things I listed. In other words, in my experience fish seem happier/healthier/less disease prone/bigger appetites when the water is renewed in a major way.

Now again, if you're seeing 50% water changes as being this huge change in your water chemistry, I think you're doing your water changes wrong. You should be able to do a change without affecting the big three things that VISIBLY cause issues with your fish.

To use your example... would you rather never go to another country because it makes you feel a little off for a day or two? Or would you rather feel a little off and enjoy all the benefits traveling can provide?

Personally, I love to travel I leave Alaska yearly otherwise I couldnt stand the winters.

Anyway, two different sides with a similar outcome. One way provides cleaner water on average than the other way, but is riskier if done wrong. I switched to large water changes after seeing someone I respected in the hobby a long time do it, I did the math and mathematically the water averages a cleaner state, and after I tested it out I continued doing it because it's easier and so far I have seen no harm to my livestock, including my delicate inverts. Right now I just have a damsel, a cleaner shrimp, some bristle stars, some tube works and some button polyps. Oh yes, and my mantis shrimp, cant forget the star of the show. None of them are complaining, visually, of my monthly water changes. Everyone is growing and happy and healthy, so I'm happy with the system I'm using.

The hobby constantly evolves. 15 years ago everyone said bioballs and under gravel plenum filters. Now those are seen as huge problem causing agents and people cant even believe they were the mainstay in the hobby just a decade past. Maybe in 10 years, everyone will advocate large drastic water changes... who knows

 

[humaguy]

in my 125, I do a 45 gallon wc every 3-4 weeks...
in my 250, I do a 55 gallon wc every 3-4 weeks...
in the 800, I do a 110 gallon wc every 3-4 weeks...

it works, and my fish love it...250 is almost 20 years old....125 is almost 10 years...and the 800 is only a few months old...
fowlr, heavy bio-load, mainly trigs and angels....