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Discussion Starter · #1 ·
Hi- new here; I've had tanks on and off since I was a kid, got back into it after a hiatus. Plant nutrition is my specialty, albeit in a different context (plant tissue culture), and I'm a chemist by training.


I've been mulling over water changes recently. Living in the desert, the water out of the tap is pretty lousy, TDS at several hundred ppm. RO helps, of course, at the expense of several gallons of reject water for every gallon produced.


For the first time in my life, I have a large-ish tank (120 gallons), with a sole occupant (an oscar) that is more or less leaving the plants alone. While I am certain some morning this will mean a rude awakening, he's never been much into landscaping, so between robust, fast-growing plants and careful planting among heavy rocks, maybe I'll be pleasantly surprised.


But the reason I write is that I would like to know: why water changes? Obviously, we need to keep nitrogen and phosphorus at bay, but provided biological filtration and careful use of plants to keep these parameters in check, what else needs to be controlled in order to keep fish healthy? I would like to reduce the amount of water used for water changes (as above- living in the desert).


Say I could add only distilled water (a real possibility, given a solar still). What are the limiting factors in this context?
 

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In our aquaria, we have bacteria, plants and fish using up nutrients and giving off by-products. Without water changes, some things can get depleted (although, can be replenished with ferts) while other substances can build up, both inorganic and organic. Oscars are notoriously messy fish.

While many of these issues can be addressed by adding nutrients and utilizing activated carbon (among other techniques), to me it is just simpler and easier to perform regular water changes and siphon out accumulated detritus.

Most recommend a minimum of 20% water changes per week, so in your case that's 24 gallons. That's not much. Your change water can be recycled somewhat by using it to water your indoor or outdoor plants. My plants thrive with old aquarium water
 

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You're not doing co2, correct?

In a low tech setup it should be doable to go atleast awhile. I would think with an oscar the concern would be dissolved organics and nitrates. As @Mark Fisher mentioned, you could go the chemical media route but then how do you handle the accumulation of detritus?

Assuming you would be adding nutrients for plants, keeping an eye on Gh, etc.

There's a thread over on Monster Fish Keepers, that I unfortunately couldn't find here real quick, that chronicles the use of Pothos to prolong water changes. I was reading it early last year so my recollection is fuzzy but I think he went atleast 6 months, if not longer. There are a ton of posts with a lot of people chiming in. Maybe you can find it? I'll keep looking as it's an interesting read.

As for RO, if you piggy back multiple membranes and add a booster pump (optimum pressure) you can approach 1:1 waste ratio. Not the same as a still but you would be able to handle much larger volumes of water.



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Discussion Starter · #4 ·
No CO2. I'm lazy about CO2, I have one planted guppy tank with a passive CO2 "diving bell" that gives me plenty of growth; I figure anything that is robust enough to survive an oscar is going to be less impressed by added CO2: zenkeri water lily, a giant Amazon sword, giant val... they'll all do *better* with added CO2, but I'll be happy enough if they hold their own as it is. Plus, I get a little angst-y about poisoning him just by trying to get plants to grow better.

>how do you handle the accumulation of detritus?

I don't mind Pythoning 1-5 gallons on the weekend to keep the gunk to an acceptable level. If the plants *do* well, then perhaps I will have to increase that volume change to keep up with abscission and damage. Right now, I can't even get the val to do anything. The zenkeri is going to take over the tank, and it's just in a 4" pot.

Things have come so far since I was last in this hobby. The water lilies we had decades ago were limited to a couple of dwarfs, and there was no LED lighting and the fluorescent lighting was just dismal. The Python is a brilliant tool, but I wish they made one with a slightly smaller acrylic tube that was longer. So many different plants to choose from today!

So, I see "organics" tossed around, and- being a chemist- I was hoping to explore that a bit more; I saw "hormones" tossed about in one discussion, but that seems glib. I'm just looking for a better classification of these compounds that seem to make the water "stale," necessitating water changes.

I've seen pothos and other plants used by Big Rich at Ohio Fish Rescue, and I've absentmindedly wondered if there are any other plants that are more efficient; I know water hyacinth (the bane of tropical waterways) is absolutely *amazing* at taking out dang near everything from water. Water lettuce probably isn't far behind.
 

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The short answer is you don't need to change water as much as folks around here suggest. If you want to grow fancy plants it becomes more of an issue but if you just want to keep your fish alive and don't care much for aesthetics, the water changes aren't really necessary. As I'm sure you know excess nitrogen and phosphorous can lead to eutrophication and anoxia, but fast growing plants can do a lot to mitigate that buildup.

If you want to know the science behind fish waste production you should be looking at papers on intensive aquaculture, not trolling a hobbyist website. The organics produced are quite literally fish poop: "Main pollutants produced per kg food fed per day were ammonia 31–37 g; phosphate 5.2–5.9 g; nitrate 9–15 g and suspended solids 40–9O g. Expressed as g kg−1 fish produced per day ammonia ranged from 0.3–0.8 g; phosphate 0.067–0.17 g; nitrate 0.13–0.21 g and suspended solids 0.80–0.94 g."
Clark, E.R., Harman, J.P. and Forster, J.R.M. (1985), Production of metabolic and waste products by intensively farmed rainbow trout, Salmo gaivdnevi Richardson. Journal of Fish Biology, 27: 381-393. doi:10.1111/j.1095-8649.1985.tb03187.x
Buildup of these wastes can cause acidification of the aquarium water. Oscars, being South American cichlids, probably would not care too much about acidic water. But just in case you try to raise guppies in the same way, it's something to be aware of.

This is also the first time I've heard someone say hormones are glib which I though was pretty funny! Fish do produce and excrete hormones, just like most living things. They can also have sensitive endocrine systems that are affected by hormones in the water and can lead to differential fertility, intersex development, etc. Vajda et. al. had an interesting paper on the effects of estrogen from a wastewater treatment plant on fish in Boulder Creek where the water at least looks very clean (I went to school there). From a plant perspective there are also the potential for unidentified allelopathic chemicals that water changes seek to get rid of. I've never heard of any specific aquarium plants that have been identified as exhibiting allelopathy, but it's certainly not outside the realm of possibility.

Most people on this website are obsessive over their tanks, and frequent large water changes make a tank look better. That doesn't mean they are necessary.
 

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I've seen pothos and other plants used by Big Rich at Ohio Fish Rescue, and I've absentmindedly wondered if there are any other plants that are more efficient; I know water hyacinth (the bane of tropical waterways) is absolutely *amazing* at taking out dang near everything from water. Water lettuce probably isn't far behind.
Maybe look into all the different Salvinia's. More "fish tankesque" than water hyacinth, if that's a thing?

One problem I have with them is their roots. Some people like them. I find they get in the way of the look of the tank.

Of course you could always treat this like a reef tank and have a separate "sump", not necessarily under the tank, that houses those kinds of plants that scrub the water.

If the idea of a "sump" sounds intriguing. Look into bog filtration for ponds. Just adapt it on a smaller, maybe more tropical, scale for your tank.

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I have an interesting "problem" in my shrimp tanks at the moment since having switched to RO water and the tanks having nicely matured and settled. The problem is this:

I can't do water changes because my water is already too clean! 0:)

To be more specific, I want to do water changes to vacuum the tank, suck out leftover food, suck out (nice green shrimp food type) algae that I clean from the front glass, etc. But my TDS remains really low, so I don't want to do water changes to lower it further. My KH and GH are spot on so I don't want to increase TDS with additional minerals in the w/c water, I just want the TDS to rise a bit through normal addition of ferts, food, leaves and driftwood breakdown, etc. But it really doesn't budge, even with full on Seachem dosing at 250% N, 200% P and 100% K plus Flourish and Trace (based on Seachen recommended dosing), adding liquid "leaves and bark", having big bits of driftwood, lots of leaves, etc, etc.

The only plants in these tanks are lots of Christmas moss and salvinia - I believe it is salvinia minima. Even with the fert dosing, I rarely get a reading for nitrate and never any sign of phosphate in any of the tanks at the end of the week. The reason, I think, is the salvinia which seems to suck up everything from the water column!

My plan was for weekly 5-10% water changes, but even after 2 weeks that seems unnecessary at the moment, so I'm now looking at a minimal water change about every 3 weeks. So, what I am trying to say is.... get some salvinia if you're looking to extend time between water changes! (at least from an excess ferts point of view). The roots of the variety I have (Minima?) extend about an inch down into the water so not at all intrusive. I love the lush green colour, shrimp like to hang from it and eat it as well as from it, it grows super fast but is easy to remove and manage, and creates nice areas of shade in the tank below to help prevent algae. It is somewhat overgrown in the photo below - normally I keep it outside the black floating ring - but the tank is full of shrimplets at the moment so don't want to risk removing anything in which they might be hiding.

 

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Discussion Starter · #8 ·
If you want to know the science behind fish waste production you should be looking at papers on intensive aquaculture, not trolling a hobbyist website. The organics produced are quite literally fish poop: "Main pollutants produced per kg food fed per day were ammonia 31–37 g; phosphate 5.2–5.9 g; nitrate 9–15 g and suspended solids 40–9O g. Expressed as g kg−1 fish produced per day ammonia ranged from 0.3–0.8 g; phosphate 0.067–0.17 g; nitrate 0.13–0.21 g and suspended solids 0.80–0.94 g."
Clark, E.R., Harman, J.P. and Forster, J.R.M. (1985), Production of metabolic and waste products by intensively farmed rainbow trout, Salmo gaivdnevi Richardson. Journal of Fish Biology, 27: 381-393. doi:10.1111/j.1095-8649.1985.tb03187.x
Ammonia, phosphate, and nitrate are not organic molecules. I can't see what they're referring to as "suspended solids" as my institution only goes back to 1997 with that journal.
 

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There are people who run tanks with little water changes, like even every 6 months or so. I don't see why it would be an absolute rule that you have to do water changes. If you can keep parameters in order, particularly across a broad enough set of parameters, there is no need. If you can explain any TDS - (GH + KH) differences then you know what is in your water.

Water changes are helpful to "reset" your water column when you feel you cannot explain everything that is in the water. For example, currently I don't trust all my water tests such as the API Master kit. I get somewhat consistent readings but with many outliers. My GH rises a little over time I think due to the Seiyru stone I used in hardscape, but can't be sure. So there are a few reasons I don't know exactly what's in my water column yet and so I use water changes as a reset, to have something resembling a repeatable baseline to start from. They also help when you are titrating dose, for example if you dose too much or in an imperfect balance and notice some algae, a fast way to correct is to reset the water column and try again.

You can use your distilled water to either mix in with tap to create your own special brew or mix some buffer with the distilled.

Bump: forgot to mention, I had considered looking at a Brita to reduce GH/KH. My water (from Potomac River) can fluctuate and is sometimes high TDS like > 400ppm. Currently it's at a nice 230ppm so I did not have to execute this plan. But I figured out that in my 50 gallon setup, I only needed a few gallons each water change from a Brita, mixed back in with tap, to drop my TDS from 400+ into a slightly more desirable range. I did not verify the Brita works but posts and their website claim it removes a significant amount of calcium and other things that contribute to my TDS ppm. It's not a perfect fix, and not sure its workable on a 125 gallon tank if you have to drop your TDS a lot, but it's much quicker to get setup than RO and does not waste the ungodly amount of water that RO does. It doesn't waste any.
 

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Ammonia, phosphate, and nitrate are not organic molecules. I can't see what they're referring to as "suspended solids" as my institution only goes back to 1997 with that journal.
See if they have a logon.
https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1095-8649.1985.tb03187.x
https://www.semanticscholar.org/pap...rman/8f45742f8a300675263e12cac05eedf51c923f38

:)

sometimes the pay wall can be breeched on line ..legally.

Research gate just requires registration I believe..
https://www.researchgate.net/publication/284425485_Nitrogen_and_phosphorus_waste_in_fish_farming

Here saved you some time, downloaded from Researchgate:
http://www.qualiteitems.com/images/waste.pdf
 

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I am aware that ammonia, phosphate, and nitrate are not organic molecules, but they are what is most important as fertilizers and for fish health. The "suspended solids" are fish poop. If you're looking for the specific chemical composition of fish poop, it probably contains a cocktail of carbohydrates, lipids, proteins, nucleic acids, live and dead gut bacteria, etc.

Bump: I am aware that ammonia, phosphate, and nitrate are not organic molecules, but they are what is most important as fertilizers and for fish health. The "suspended solids" are fish poop. If you're looking for the specific chemical composition of fish poop, it probably contains a cocktail of carbohydrates, lipids, proteins, nucleic acids, live and dead gut bacteria, etc.
 

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I am aware that ammonia, phosphate, and nitrate are not organic molecules, but they are what is most important as fertilizers and for fish health. The "suspended solids" are fish poop. If you're looking for the specific chemical composition of fish poop, it probably contains a cocktail of carbohydrates, lipids, proteins, nucleic acids, live and dead gut bacteria, etc.

Bump: I am aware that ammonia, phosphate, and nitrate are not organic molecules, but they are what is most important as fertilizers and for fish health. The "suspended solids" are fish poop. If you're looking for the specific chemical composition of fish poop, it probably contains a cocktail of carbohydrates, lipids, proteins, nucleic acids, live and dead gut bacteria, etc.
Fish poop would break down into constituent components at some point though wouldn't it?
 

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Fish poop would break down into constituent components at some point though wouldn't it?
Maybe some of it would, but not all. That's what mulm is. It might be somewhere you can't see it (i.e. in your gravel or in the filter) but there are many organic compounds don't just spontaneously decompose in water.

Stole this from the paper @Mark Fisher posted as it's both relevant and interesting:

Solid wastes are primarily derived from the uneaten feed and fecal droppings of cultured fish (Akinwole et al., 2016). They occasionally include those fish that do not survive the culture process. Solid wastes can be further classified as suspended solids and settled solids. The suspended solids are fine particles and remained suspended in the water, except when a method of coagulation or sedimentation is employed, and are the most difficult type of solids to remove from culture systems (Cripps & Bergheim, 2000). The settled solids are larger particles that settle within a short period of time and can be easily removed from the culture column (Ebeling & Timmons, 2012). Solid wastes have been classified as the most dangerous waste in fish culture systems and should be effectively removed as quickly as possible (Timmons & Summerfelt, 1997). Solid wastes are regarded to be very dangerous because they can clog the fish gills and lead to death, especially in the case of large settled particles (Akinwole et al., 2016). If left for a long time and allowed to decompose, these wastes lead to increases in both the total suspended and total dissolved solids. They may also increase the nitrogenous compounds and stress the cultured fish (Akinwole et al., 2016). If solid wastes in aquaculture remain within the culture system, their aerobic bacterial activity will increase the chemical oxygen demand and biochemical oxygen demand and deplete oxygen within the culture column (Timmons & Lorsodo, 1994).
 

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Other than having likely a lot of dissolved minerals, resulting in high TDS, what else about your tap water makes you think it's poor quality? Does it also have high phosphates/nitrogen content - or other impurities that make it low quality? If it's simply hardness, that shouldn't make the water quality "poor" unless you're keeping plants/fish/shrimp that absolutely require soft, more pure water.
 

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But the reason I write is that I would like to know: why water changes?
I have a question for you, how would you like to swim your whole life in your own feces?
Or more realisticially how you would like to live and swim in mechanically filtered sewer water?

From one chemist to another I really hope you realize bacteria and a mechanical filter do not completely 'clean' water.
 

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I have a question for you, how would you like to swim your whole life in your own feces?
Or more realisticially how you would like to live and swim in mechanically filtered sewer water?
Sorry, but I think you have completely misunderstood / misrepresented the OP's question here, especially by quoting a few tongue-in-cheek words of the original post out of context.

The question was to understand what the limiting factors are regarding the necessary amount and frequency of water changes, and this is a very valid question and one which I would certainly like to know the answer to too! The OP asked from the context of needing to conserve precious water, I'm interested because water changes are often considered bad for shrimp tanks because they can upset stability.

So, let me rephrase the question:

Let's say I have a tank where the water looks crystal clear (i.e. no suspended 'dirt' or algae etc), the substrate has no build-up of mulm, the water tests at zero ammonia, nitrite, nitrate, phosphate, iron and every other possible contaminant for which there is an aquarium home test kit readily available. The GH and KH are exactly where they should be and TDS is only marginally above that resulting from the desired GH and KH components. The plants are growing well and the livestock are healthy and breeding.

Is there an unknown or undetectable (within the capabilities of our home aquarium resources) substance that might be "polluting" this otherwise pristine looking water and which makes a water change necessary? If so, what is it, what is the critical level and how would we know when the tank reaches it?

Suggestions so far in this thread seem to be that hormones may buildup. Anything else?

If you are happy to do a 50% weekly water change then great, sure that happily resets everything (but, to be clear, the fish are still swimming in 50% diluted sewerage!). But why 50% and not 60%, 30%, 5% or some other arbitrary value? And why weekly and not daily, or bi-weekly or monthly? It's a bit like EI dosing - add more ferts than the plants will ever need and you can be sure they won't run short - easy, anyone can do that! But being able to dose the exact amount of ferts the plants need that week without wastage or deficiency, that takes more knowledge, experience and understanding than most of us will ever have!
 

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Before the Walstad method was popular I had read her book where she claims she goes more than 6 months between water changes on some of her tanks:

"The hallmark of a Low-tech aquarium is that it is easily maintained. Aquariums seem to do well without hobbyist adjustment, maintenance, and cleaning. For example, my own aquariums often go for six months or more without water changes. Fish get fed well, so that plants do not need to be fertilized artificially. The only routine maintenance is replacing evaporated water and pruning excess plant growth. Tanks that are unbalanced need constant cleaning and adjustment."

Walstad, Diana Louise. Ecology of the Planted Aquarium: A Practical Manual and Scientific Treatise . Echinodorus Pub. Kindle Edition.

She does prescribe water changes when first setting up tanks to deal with initial ammonia and nitrite spikes.

As another point, fish that live in ponds are essentially swimming in their own sewage all day long. Ponds may not cycle water through very quickly if at all, just refilling from rain overflow or a spring.
 

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Discussion Starter · #20 ·
Other than having likely a lot of dissolved minerals, resulting in high TDS, what else about your tap water makes you think it's poor quality? Does it also have high phosphates/nitrogen content - or other impurities that make it low quality? If it's simply hardness, that shouldn't make the water quality "poor" unless you're keeping plants/fish/shrimp that absolutely require soft, more pure water.
The water we have here in Phoenix is a combination of surface and subsurface water; the surface water does not have issues with nitrates nor phosphates. It's remarkably good (other than aesthetic concerns which get quite complex) but for the high TDS- mostly sodium, sulfate, chloride, etc.- a bunch of ions that aren't really useful in the context of aquaculture. But, of course, without running a controlled experiment, I am unable to say whether there would be any positive results would that I were to use water with lower TDS.

An example: a 55-gallon with a single 2" oscar (a freebie from a big-box store that, at the time, was in danger of being an ex-fish), and there is virtually no evaporation; with 10-15% water changes every week, TDS is over 1000 ppm as measured with a digital TDS meter. That's how bad it is here. As a kid, when I had more fish, we had 80 ppm TDS right out of the tap, and that was mostly carbonate hardness. At least the fish could make do with the calcium.


If you are happy to do a 50% weekly water change then great, sure that happily resets everything (but, to be clear, the fish are still swimming in 50% diluted sewerage!). But why 50% and not 60%, 30%, 5% or some other arbitrary value? And why weekly and not daily, or bi-weekly or monthly?
I think this is an excellent way to put it, thank you.

We rely upon test kits and meters for ammonium, nitrite, nitrate, pH, hardness, and temperature. Once these are satisfied, what other parameter(s) may fall out of whack, and how do we measure them to optimize the conditions for our charges? If I can't measure it, is it even a real concern?

If it's hormones, OK- I'll throw up my hands and keep doing water changes rather than purchase that $180,000 LC/QQQ for measuring salmon gonadotropic-releasing hormone, I totally get it. Y'all are the gurus at keeping semi-closed system aquaria, I'm not trying to come off as some sort of a jerk. Scientific curiosity has gotten the best of me, and I appreciate the discussion thus far.
 
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