Big, weekly water changes. Good idea or not?

[Masha]

Okay, I know this is a little bit of a hot topic, so I hope I'm not stirring up trouble by asking about it.

I see some conflicting advice about water changes. Now - granted - every tank is different, and somebody keeping discus is going to need to have a different water change regimen that somebody keeping a tougher fish like black widow tetras, for example.

But as a general rule - what do you think is the ideal water change regimen?
I see some people say 50% a week. Then I see other saying that will result in drastic changes in the water chemistry which is bad for the fish, and smaller, more frequent changes are better.

I can imagine that if you let your tank stand for a month or so and then suddenly do a 50% change, there would be a big difference between the tank water and the new water coming in. But if the changes are done weekly, is that really something that will stress fish?

And I mean "fish in general" if there is such a thing not special cases of more than usually sensitive fish. Is it this a "how long is a piece of string" kind of question that differs from tank to tank, or is there a rule of thumb that most of us can follow?

 

[JohnRoscoe]

I do 25% weekly bc I have a 16 gallon tank, and 4 gallons in a 5 gallon bucket is easy to move without spilling. When I've had problems, I change more often, but not more volume. My tank is planted, not heavily stocked, and very healthy right now. I could probably get by with less but why stop a good thing.

It's important to be practical. If I had a 50 gallon tank, I'd make it my goal to get down to 8 gallons changed at a time, because that's only 2 buckets. I should note that I work from an RO tap in the kitchen, so I'm never going to be a hose-fill guy.

 

[Masha]

JohnRoscoe, that's a good point.
I bet bucket-change people like me are going to have a different water change % than people who can easily change high volumes with a hose setup...

And I like your approach of "change more often, but not more volume" that makes sense to me.

Up till now, I've changed 50%, but now I've got a setup where I'm treating, aging and heating the water so it's EXACTLY right before I pump it into my tank - and that will all be easier if I do about 25 - 30% because that's the size of the bucket I'm storing the water in.

 

[gilpi]

As far as I'm concerned, the more water changes, the better. It wasn't till I started years ago changing water more aggressively that I saw my fish healthier with a faster growth rate.

 

[Delapool]

As a small experiment, I changed out 90% of the water each week and there was a temp drop of 5C. This was in a small 5gal and I thought the fish was actually doing better than in the DT with 30% changes each week. Which didn't really make sense as that is a large change in water and temp.

Gone back to doing 50% changes and temp matched (roughly) for small tank. My theory is consistently the same water change is best although I've settled on 30 to 50% for preference.

I've noticed with sick fish that you can get them to perk up on a decent water change. And a water change is often suggested as well.

On new fish not coping well, I prefer not to water change so much and let the fish settle. Still working on that idea Thoughts anyways.

 

[gilpi]

Matching temp is definitely a must when doing water changes. Since I have multiple tanks I use a hose right from the faucet (after treating the tank with prime) and I go by feel, I'm usually within +/- a couple of degrees.

 

[PerfectDepth]

In my opinion, if you have good tap water, there's no reason not to. It's especially important for smaller tanks.

I think it's somewhat of a misconception that frequent, large water changes are stressful to fish. Water changes are not stressful at all, but changes to the water are. TDS (total dissolved solids) and pH etc. should remain fairly close to the source water as long as large water changes are done on a regular basis.

As long as the temperature is fairly close, fish actually seem to love water changes. In my experience, they become more active and even tend to show spawning behavior, especially right after large changes of 50% or more.

If you wait too long between changes, a large water change can absolutely be harmful to your fish, but only because the water in the tank has a build up of dissolved organic material, and the quick change in TDS shocks your fish. If that's the case, and there's an emergency situation or you're trying to bring down the level of nitrates, instead of being able to just do one or two large water changes, you're forced to do a lot of small water changes first, which is a huge PITA. That's why large, frequent water changes are the best practice, in my opinion. However, there are different tank situations, and not everyone has suitable tap water, so you have to choose the routine that works best for your situation.

 

[Coyne]

I have a small, clear piece of tape discreetly place in a corner at the half way point on all my tanks so that I can tell at a glance when I've removed 50% of the water during the weekly PWC.
I think if you factor in water displacement from substrate and decor, then it's probably closer to 60%. Once every other month I'll do a bigger, 90% PWC to better clear out that slow nitrate build up that occurs.
I do think size does matter, but frequency and consistency might be slightly more important IMO. Best if you can cover all the bases though.


Sent from my iPhone using Aquarium Advice

 

[Masha]

Water changes are not stressful at all, but changes to the water are.

That is a good way of putting it. I find it hard to know what is stressful to my fish - I mean, sometimes I can tell they are freaked out about something, when they hide, or go pale, but as a general rule I don't always feel confident that I know when they are stressed.

 

[PNWaquarist]

If you refrain from overstocking your tank, there is usually no need to do 50% weekly water changes.

 

[PerfectDepth]

Maybe I shouldn't say water changes aren't stressful at all- of course fish are going to get a little stressed, it's unavoidable. I just try to be careful to make the process as stress-free as possible and not accidentally corner a fish with the gravel vac for example. I will say that even lights turning on or off seems to spook them just as much if not more than the lowered water level and general messing around in the tank that's involved with tank maintenance. Or at least they seem to bounce back way more quickly after a water change vs. a lighting change.

 

[PerfectDepth]

If you refrain from overstocking your tank, there is usually no need to do 50% weekly water changes.

I would say it depends on the particular situation.

For example, a 10 gallon or smaller tank would definitely benefit from large weekly changes whether it's lightly or heavily stocked. Smaller volumes of water have a smaller margin of error, i.e. problems can creep up much more quickly, and though weekly 50% water changes might not be absolutely necessary, it's just a good preventative measure to help keep the water conditions stable.

Another example: discus keepers often stock very lightly, but still change massive amounts of water. Sometimes 50% or more daily (not weekly). This sort of dispels the myth that large water changes will affect sensitive fish, since discus are one of the most sensitive fish in the hobby.

 

[SFAquariums1]

I don't think discus, as well as other types of fish, fall into the catagory of "normal fish" like the op asked. Discus has it's own water change schedule...

I personally don't see why a 10 gallon tank with say 6 neon tetras, some live plants, and a substrate would need anything more than 20 percent water changes each week.

With that being said if appropriate stocking levels are kept, water changes shouldn't need to be as large. Obviously there are always special circumstances.

In my personal opinion, I don't feel like there will ever be a 100% cut and dry answer to the question of how much water to change.


Sent from my iPhone using Aquarium Advice

 

[PNWaquarist]

I would say it depends on the particular situation.

For example, a 10 gallon or smaller tank would definitely benefit from large weekly changes whether it's lightly or heavily stocked. Smaller volumes of water have a smaller margin of error, i.e. problems can creep up much more quickly, and though weekly 50% water changes might not be absolutely necessary, it's just a good preventative measure to help keep the water conditions stable.

I agree, and should've added this caveat.

Another example: discus keepers often stock very lightly, but still change massive amounts of water. Sometimes 50% or more daily (not weekly). This sort of dispels the myth that large water changes will affect sensitive fish, since discus are one of the most sensitive fish in the hobby.

As I've mentioned before (but not in this thread), there are exceptions and I've used GBRs as an example. Discus are a more extreme example of that. In these cases, the chemical stress of large water changes is outweighed by their need for < 10 ppm nitrates.

On the other hand, the fact that many discus owners change 30-50% of their water twice a week also minimizes the chemical difference between tank water and tap water. (Three-day-old tank water is not that chemically different than fresh tap water.) So there's inherently less chemical stress in a situation like that than in a more typical situation with weekly (or bimonthly) water changes and less nitrate-sensitive species.

(And I have a difficult time seeing how those who change out 50% of their tank water every day can enjoy their hobby. It seems more like a chore to me at that point. But that's JMO.)

In general, I think it's fair to say that if you need to turn over large volumes of water in your tank for whatever reason, it should be done frequently to avoid abrupt changes in water chemistry. Doing 30% changes every week is preferable to doing a 60% change every other week.

 

[Andy Sager]

As previously stated, it's not the amount of water that one changes that's detrimental but the amount of change in the water that's being added back that needs to be addressed.
I've kept many tanks over the years of varying sizes and my routine water change schedule was/is 10%-15% of volume weekly. Just by doing that and keeping tanks understocked, the need to change more than that amount for nitrate control wasn't there. The only exception to this was my breeder pairs of Oscars. They were extremely messy fish so they got more frequent water changes ( as well as over sized filters). But again, it was frequency over volume.
As with everything, there are going to be exceptions. The examples above of Discus and GBR hobbyists brings out the point that if you change large volumes of their water BUT add back in similar water ( sans the nitrates) the fish should do fine. Try changing those water parameters above & beyond the 0 nitrates and you will probably see a tank of dead fish. "Not the volume of the water, the change in the water."
If you are dealing with a single tank or just a couple of tanks, it may not be any hardship to do larger changes but doing so on multiple tanks, it's certainly a task not desired. In one of my previous hatcheries, I had 400 tanks going. Can you imagine the work involved in changing that much water weekly? That was just using the 10%-15% standard. I produced quite a number of fish doing it this way so it must have worked. There is another factor to changing smaller volumes of water, IF there is a change in parameters, due to the smaller volume of change, the fish are less likely to be adversely effected. So, for example, in a 10 gal tank, if you add back 1 gal of water that is of a different PH value greater than .2 ( the recommended amount of change in a 6-12 hour period) , it's not going to drastically change the PH in the rest of the tank. If you add back 5 gals, it definitely will.

I still hear my Mentor's favorite saying( Keep in mind he was a certified Ichthyologist, 12 years of training for his degree) , " If your water changes that much in a week's time that it's not safe for the fish to live in, you are either overstocked or under filtered. FIX IT! " I still follow that rule 50 years later. I just keep a nitrate test around for giggles. Never really need to use it

Hope this helps

 

[PNWaquarist]

Well said, Andy.

 

[BillD]

While a minimum amount of water needing to be changed can be determined with a nitrate test, changing more allows you to stay ahead of the curve. As well, what was fine when you started the tank, is likely to be insufficient 6 or 8 months down the road when the fish have grown.
I would be curious to know where the .2 pH change in 6 to 12 hours came from. CO2 injected tanks may experience far more than that twice a day. I stopped testing for pH years ago.
As already well stated, the more often you change the water the less likely there will be any significant difference between the tank water and tap water. From my limited experience raising angels, I have seen the difference clean water makes to growth rates and appearance of the fish. Miss a couple of changes and the entire spawn can be ruined.

 

[Masha]

Now...the problem I have with the "you only need to do large changes if you overstock" thing is this: we all seem to have rather different ideas of what overstocked means. It's not that straightforward is it? I've seen people say:

"as long as nitrates stay below x"
"1 fish per gallon" (or whatever that rule is, can't remember now)
"what aqua advisor says"
"It just looks too crowded in there"
"well, they're not actually dying right now so they must be fine."

But it really depends on such a complicated balance between the type of fish, size of tank, surface area, amount of filtration, amount of feeding done etc, etc that "don't overstock" is just not very helpful advice.

I mean, it's not just about water quality, is it, it's also about swimming space, enough companions of the same kind of fish together, how aggressive a particular fish is...and even if you do focus only on water quality, what about the stuff our home tests cannot measure? I've seen people argue that just going by the nitrate levels is not enough, your tank might be full of all kinds of other chemical or hormonal substances that are harming your fish.

Which is kind of frustrating because you are left with "do large water changes just in case, who knows."

 

[JRT83]

I have 1 10" male jaguar cichlid in a 125 gallon tank and can say from 2 years of experimenting with different water change schedules that his colors get washed out and he gets stressed when I do anything above 30-40% at a time. So I've stuck to 2 20-30% water changes per week and sometimes my nitrates won't even reach 5ppm in between water changes. I'd say consistency in water parameters are far more important than doing random 50+% water changes for no reason.

Sent from my LG-E980 using Aquarium Advice mobile app

 

[Delapool]

Now...the problem I have with the "you only need to do large changes if you overstock" thing is this: we all seem to have rather different ideas of what overstocked means. It's not that straightforward is it? I've seen people say:



"as long as nitrates stay below x"

"1 fish per gallon" (or whatever that rule is, can't remember now)

"what aqua advisor says"

"It just looks too crowded in there"

"well, they're not actually dying right now so they must be fine."



But it really depends on such a complicated balance between the type of fish, size of tank, surface area, amount of filtration, amount of feeding done etc, etc that "don't overstock" is just not very helpful advice.



I mean, it's not just about water quality, is it, it's also about swimming space, enough companions of the same kind of fish together, how aggressive a particular fish is...and even if you do focus only on water quality, what about the stuff our home tests cannot measure? I've seen people argue that just going by the nitrate levels is not enough, your tank might be full of all kinds of other chemical or hormonal substances that are harming your fish.



Which is kind of frustrating because you are left with "do large water changes just in case, who knows."

Well, I must admit I've been thinking it is the types and amount of each stress type that would be good to understand more.

So maybe you do a 50% pwc (stress A), it's 2C difference (stress B), no nitrates/phosphates (stress C).

I assume there is a tipping point where the fish says stuff-it. So we don't go above that point. But is each stress type of equal weighting, etc, etc?

So a large water change is fine (little stress),

large water change + ph change (little stress),

as above + gh/kh change (too much stress on fish).

I guess what I'm getting to is that consistent water changes are fine but what do we look for as a consistent water change (what's most important)?

I would guess it would be gh and TDS??