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Question of the Day Why are we doing water changes???

Art

Owner/Administrator
Staff member
Supporting
Founding Member
PAFF
  • Oct 29, 2022
    2,153
    2,402
    Miami, FL
    Good morning and happy weekend, ScapeCrunch family!

    Today's question of the day is interesting to me. There are nuances to it so please be honest and don't necessarily go with your first reaction.

    Assume you fertilize lean (providing very little excess nutrients from perceived plant uptake) AND you are running activated carbon (or AquaChar ;)) that is effectively removing the dissolved organic carbon from your water, would you still do weekly water changes?

    Answers don't count unless you tell me the why with your choice.
     
    I think the answer to this question is pretty simple...

    You do water changes to reset your nutrient levels, which is still important even in a lean fertilized tank. Based on what I've seen, people are just adding a couple squirts of this or that based on their observations, but a squirt isn't an exact measurement so without testing you really don't know how much you're actually dosing. It also helps with accumulation of nutrients. I generally do pretty large water changes, and until more recently the ever increasing levels of NO3 and PO4 I thought were coming from somewhere, but they're just what remained even after water changes of 80% or larger.

    You also do them to export solid waste - decayed plant leaves, fish poops, etc. This stuff needs to be manually siphoned out.

    The last reason is any dissolved organic compounds can be removed through a water change.

    I remember having a debate about the value of water changes a while ago and there's really no way to get around them. This should be a factor that people take into consideration when they get into a planted tank.

    Hypothetically the only way to get the benefits of a water change without actually changing your water would be to pump your aquarium water through a reverse osmosis filter, but then somehow not have any waste water.

    I have seen people's tanks who claim to do no water changes except topping off evaporation, but they never take close ups of the tank and plants, and for good reason....we'd all see algae :LOL:
     
    Same here, reseting the nutrients levels, get rid of solid wastes or detritus specially if I am vacuum cleaning the gravel as well and finally refreshing the water in the tank, in general we are trying to create an echo system in a very small closed container compared to nature, in rivers and lakes water is frequently refreshed through rain and other means, but in our closed echo system the only means of refreshing the water is by changing from 25% to 70% or even more in some cases, regarding algae I believe refreshing the water is a good thing to preventing and reducing algae spores in the water

    Having said that I do tried before a small 50 cm tank with no water change for months, just topping the water and everything was fine, the tank hosted a very low bio load with a huge number of plants and everything was fine and it was the single tank with almost no algae
     
    The fish animals we keep live in streams and rivers and never live in a trapped water environment that we place them in. So it is best to change water to keep them is a constant safe nutrient level environment.
     
    So I agree with you guys. What I'm trying to get at is just to get people thinking.

    I think ICP testing will become an easier thing to do in the future. There will be a push to use it to really dig deeper into the how, why and what of fertilizing. This will make us re-think the why's of our water change routines.

    I agree we need to find a way to remove detritus. However, please know that GAC will remove DOC from the water column better than a water change. A 50% water change will take out 50% of the DOC in your water. GAC will remove 100% with no water change.

    One challenge our hobby faces with new people is the weekly water change. When you tell a newcomer that they need to change 50+% of their water weekly, they get that "HELL NO!" look on their face. This is especially true if they are thinking about a larger aquarium. A 45 gallon water change??!

    Yes, we can get water changes to be easier. No doubt. This is especially true if your tap water is reasonably good. But add RO to it and now we're talking about a) making water, b) storing it and c) changing the water weekly.

    My point is there is a bit of a commitment.
     
    In my experience the single best thing you can do for a planted tank is to perform large water changes. The reality is the more the better.

    That being said the optimum amount and frequency depends on a lot on the type of tank. A lower light tank full of slow growing swords/crypts/anubias is a different animal than a high light tank full of stems and can get by with a lot less. And tanks with less fish load can by with less than tanks with more fish load.

    Every once in a while someone comes along and claims they keep a great high light tank full of stems with no water changes. When pressed for pictures they start to squirm and offer every nutty excuse you can think of about why they can't. And 90% of the time when they do post a pic, well let's just say you immediately understand why they were reluctant to do so.

    It's also pretty well known in the hobby that if you want to whip a tank into shape, perform twice a week large water changes for a few weeks to completely reset the water column. It can do wonders when people have problems.

    I agree we need to find a way to remove detritus. However, please know that GAC will remove DOC from the water column better than a water change. A 50% water change will take out 50% of the DOC in your water. GAC will remove 100% with no water change.
    I get where you are going here and this is has been under researched and underdiscussed. I am going to be experimenting a bit with this coming soon. At this time not so much to replace water changes but to see what effects it may have or may not have on the tank.
     
    Last edited:
    Of course, I agree with everything you said, @GreggZ. I do think more research is needed to get a better understanding. We should never think we have it all figured out and further improvement isn't necessary.

    While I know the saltwater side has much more sensitive creatures to worry about, they are very concerned with stability of the aquarium environment. We seem to think that a water change of 80% is just fine as we see now adverse reaction to it.

    It makes me wonder, though. No matter how much we try, the water chemistry in our water change water will never be the same as what we are taking out. Does such a large disruption cause any negative consequences?

    Anyway, no controversy here. Just thinking out loud.
     
    Of course, I agree with everything you said, @GreggZ. I do think more research is needed to get a better understanding. We should never think we have it all figured out and further improvement isn't necessary.

    While I know the saltwater side has much more sensitive creatures to worry about, they are very concerned with stability of the aquarium environment. We seem to think that a water change of 80% is just fine as we see now adverse reaction to it.

    It makes me wonder, though. No matter how much we try, the water chemistry in our water change water will never be the same as what we are taking out. Does such a large disruption cause any negative consequences?

    Anyway, no controversy here. Just thinking out loud.
    I think many of those variables can be eliminated by starting off with RODI and remineralizing.

    Assuming you're starting out with TDS 0, and then bringing it up to the Gh and Kh you are targeting, and the water is the same or close to the same temp, the one thing you're definitely disrupting are the Fert levels.

    If you can keep the fert levels the same after a water change, then theoretically you're only exporting organic compounds and other things that the fish and plants produce as byproducts.

    On the reef side, corals to one degree or another will strip Ca, Mg, and traces from the water. Assuming you're only relying on water changes to replace what the corals are stripping out, then you kind of yoyo back and forth with each water change. But if you're dosing to keep your Ca, Mg, and traces at the levels that your salt mix contains, then the same holds true that you're mainly removing the stuff you don't want. A friend of mine made sure his Ca and Mg levels were higher than his salt mix, along with various trace minerals and would do a water change effectively resetting the parameters back after a water change, and then building them up again. I kept my parameters roughly at what they were in my salt mix. Our equipment was roughly the same, except he dosed rather than relied on a calcium reactor and kalk, but was adding far more than I was even with a reactor. The difference was that my corals seemed to put on growth a lot quicker than his did. About two years ago he lost several grand in corals because he wanted to avoid water changes by using a sulfur reactor. It worked fine for a while, but then Murphy showed up with his law, and something happened with the reactor and he came home to a complete meltdown inside the tank. Sometimes a solution to a problem can have more disastrous consequences than just doing the safe thing, like a water change.
     
    Agreed. Thankfully, our meltdowns are not as epic or as costly as the reef side can be.

    The variable, of course, are 1) plant uptake levels and 2) other things in the water column that are not known to us at the moment. The controlled water change where you start with zero water and add to it, results in you having a very good idea of the input water. What you don't have a very good idea about is what's in the water you are removing. Yes, we can guess at nutrients that are being removed as a percentage of your water change. We can also guess at other things such as DOC, etc.

    Here's an example of what I'm talking about. Let's just say you use RODI water and you had a fixed formula of nutrients every week. You do a 50% water change weekly.

    Based on the above, the accumulation calculator can give you some insights. However, it doesn't factor in plant uptake of nutrients. Since you are not measuring prior to a water change, you can't tell me how much magnesium your tank consumed. Over time, the nutrients in your aquarium will not be what your calculations are.

    If what I just wrote above makes sense to you, how do you solve for it without testing?

    I realize that this may be theoretical but it may explain some of the mystery long-term issues some experience. This is not to mention the variable of your substrate. It absorbs nutrients (and other things) over time. What does that do longer term?

    If you're like me and don't like situations where you are doing something simply because it works without understanding what it's doing, then this is the stuff you lay at night thinking about. I know, I know, I'm weird.
     
    Agreed. Thankfully, our meltdowns are not as epic or as costly as the reef side can be.

    The variable, of course, are 1) plant uptake levels and 2) other things in the water column that are not known to us at the moment. The controlled water change where you start with zero water and add to it, results in you having a very good idea of the input water. What you don't have a very good idea about is what's in the water you are removing. Yes, we can guess at nutrients that are being removed as a percentage of your water change. We can also guess at other things such as DOC, etc.

    Here's an example of what I'm talking about. Let's just say you use RODI water and you had a fixed formula of nutrients every week. You do a 50% water change weekly.

    Based on the above, the accumulation calculator can give you some insights. However, it doesn't factor in plant uptake of nutrients. Since you are not measuring prior to a water change, you can't tell me how much magnesium your tank consumed. Over time, the nutrients in your aquarium will not be what your calculations are.

    If what I just wrote above makes sense to you, how do you solve for it without testing?

    I realize that this may be theoretical but it may explain some of the mystery long-term issues some experience. This is not to mention the variable of your substrate. It absorbs nutrients (and other things) over time. What does that do longer term?

    If you're like me and don't like situations where you are doing something simply because it works without understanding what it's doing, then this is the stuff you lay at night thinking about. I know, I know, I'm weird.
    No I totally get it. It's good to see that I'm not the only one that goes down rabbit holes lol.

    From the accumulation perspective, I think doing a much larger than normal water change every so often will help address accumulation. Even then you'll still get some accumulation but knowing what your plants are consuming would be huge. The challenge is understanding that with fish producing waste and plant matter decaying in the tank, and to what extent does waste trapped in your substrate affect things. I planted a few plants last night and as soon as my tweezers began pushing the plants into the sand, huge orange/reddish dust clouds of waste rose up into the water column. What that told me is that I need to do that manually during water changes going forward.

    What's a little frustrating is how readily available all manner of tests are on the reef side, but on the fresh side the options are far more limited, and even to some extent the quality of the test kits can be dubious if you do find an oddball manufacturer of an uncommon test kit. This is one area that I believe needs vast improvement. For example, look at Hanna. The vast majority of their checkers are marine checkers. From a business standpoint, they're putting their money where the most ROI is, which is the reef side. Reef is definitely a very small part of the market in comparison to freshwater. In all honesty though, that's where the wallets are much larger as well, but I'd wager a guess that planted is likely about the same market size as reef is. Even at that, how many people are going to want to test stuff other than NO3 and PO4? To test K, it seems like there's only one option, and to test for Fe, you basically have two. So it makes sense that if it's not as easy as the same reagents being manufactured as for marine, then they'd focus on the reef side since they know there will be a return on investment whereas I don't think they'd see an ROI on the planted side.

    When I started back up earlier this year, there were two schools of thought on the planted side - lean or EI. Both required 50% weekly water changes, but the former required a much better understanding of plant health to visually adjust your dosing, while the latter was like using a machine-gun to hunt doves. I went with EI because almost everyone with expertise and experience said you didn't need to test and it was idiot proof. After a decade in countless tests on my reef tanks, hearing that testing was pointless was a godsend lol.

    Honestly I think the only way to really solve the problem is through sending water samples to a lab for a full analysis of what's in the water. I've never done this myself, but I know several reef keepers who went this far and from what I remember it wasn't inexpensive.

    Honestly I think a great start would be sending a water sample off to a lab to get a full understanding of what is in the water. From there it would be easier to know what you're dealing with and make decisions on where to go next. I think the only thing that would send me down this particular rabbit hole is running into an issue that I can't solve and can't explain. That's where I was a few weeks ago. But the problem resolved itself for the most part so my assumption is that something I'm doing is working. While it does bother me that I don't know exactly what it is I'm doing that is helping, I'm not sure the costs of lab testing would be worth it unless it was $20 or some other nominal fee.
     
    Based on the above, the accumulation calculator can give you some insights. However, it doesn't factor in plant uptake of nutrients. Since you are not measuring prior to a water change, you can't tell me how much magnesium your tank consumed. Over time, the nutrients in your aquarium will not be what your calculations are.
    Yes Art I get this. But in the scheme of things I don't think knowing the exact amount of uptake would make any appreciable difference.

    Let's say we determine that in a particular tank plants uptake 2 ppm NO3 daily. Does that mean that we should dose 2 ppm daily?

    In my opinion that is a recipe for a bunch of starving dying plants. So then the next question is what is that "optimum" amount in the water column that allows for plants to uptake that 2 ppm most easily? Is it 10 ppm? 20 ppm? 30 ppm? I would argue that it depends on the type of plants, the amount of light provided, and the particular mix of plants in that tank.

    Then in addition to plant uptake you have tank generated nutrients. A lot of wild cards there like fish load, type and amount of fish food provided, maintenance horticulture/trimming habits (dead/decaying plant matter), etc.

    To me it's better to focus on the things we can control, like dosing and water changes. For folks like me that use RO and perform large regular water changes, it's pretty easy to keep relatively stable levels in the water column, and not much risk of anything accumulating to any extreme. For folks who perform small infrequent water changes it's a bit more dicey.

    All that being said I would definitely be interested in a comprehensive water test. If nothing else just for the sake of curiosity. Based on my testing I have a pretty good idea of what is happening in my tank and I wouldn't expect many surprises but still inquiring minds want to know!
     
    Yes Art I get this. But in the scheme of things I don't think knowing the exact amount of uptake would make any appreciable difference.

    Let's say we determine that in a particular tank plants uptake 2 ppm NO3 daily. Does that mean that we should dose 2 ppm daily?

    In my opinion that is a recipe for a bunch of starving dying plants. So then the next question is what is that "optimum" amount in the water column that allows for plants to uptake that 2 ppm most easily? Is it 10 ppm? 20 ppm? 30 ppm? I would argue that it depends on the type of plants, the amount of light provided, and the particular mix of plants in that tank.

    Then in addition to plant uptake you have tank generated nutrients. A lot of wild cards there like fish load, type and amount of fish food provided, maintenance horticulture/trimming habits (dead/decaying plant matter), etc.

    To me it's better to focus on the things we can control, like dosing and water changes. For folks like me that use RO and perform large regular water changes, it's pretty easy to keep relatively stable levels in the water column, and not much risk of anything accumulating to any extreme. For folks who perform small infrequent water changes it's a bit more dicey.

    All that being said I would definitely be interested in a comprehensive water test. If nothing else just for the sake of curiosity. Based on my testing I have a pretty good idea of what is happening in my tank and I wouldn't expect many surprises but still inquiring minds want to know!
    I'm going to ask some of my old reefing buddies who they used for their lab analyses. They shared the process and information with me a long time ago but in the span of 10 years that may have changed and I'm not sure where that information went.
     
    @GreggZ

    My buddy just replied, this is who they use for lab testing:

     
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