Question from a chemist about water changes - Page 2 - The Planted Tank Forum
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post #16 of 45 (permalink) Old 10-09-2020, 02:00 AM
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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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post #17 of 45 (permalink) Old 10-09-2020, 04:29 AM
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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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post #18 of 45 (permalink) Old 10-09-2020, 05:09 AM
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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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Last edited by ahem; 10-09-2020 at 05:10 AM. Reason: clarity
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post #19 of 45 (permalink) Old 10-10-2020, 04:54 AM
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Been meaning to order a copy of Walstad's book for some time, so just placed an Amazon order....


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post #20 of 45 (permalink) Old 10-11-2020, 03:19 AM Thread Starter
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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.
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.


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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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post #21 of 45 (permalink) Old 10-12-2020, 11:54 AM
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Afraid I can't help with the initial question as to what the waste products . At the end of the day everything that goes into the tank is transformed into some type of waste product, plant matter or fish, And potentially any pathogen or parasite the fish brings with it could also be a concern. I think for the largest part you are correct the numbers do tend to be arbitrary and I don't know what level of water change would be acceptable for your livestock and tank since again pollution levels are going to be dependent on inputs (creating waste products) and exports (water changes) regardless of what they consist of. The assumption I'm making here of course is that everything put into the tank would eventually be incorporated into the plants but some compounds and materials may take longer degradation paths that may or may not bottleneck. How this is captured by a TDS meter may not be applicable given the nature of the compounds? I can't say I know. At the end of the day what we do know is a 50% water change limits pollutants to twice the amount of pollutants added weekly. A 33% water change limits accumulation to 3 times, and a 25% to 4 times, et cetera. Most people with access to cheap plentiful water shoot for the lowest levels of pollution, but the absolute level of pollution is again dependent on inputs. Acceptable (to the hobbyist and the livestock) levels of pollution are another ball wax entirely. If you read old aquarium publications they suggest levels of pollution that most wouldn't find acceptable now, regardless one would assume they had success back then. Another thing to bear in mind is that you are asking a group of people who larges add a lot of inputs that people wouldn't have dreamed of historically.

Realize this probably wasn't much help, but fun for me to think through.

Good luck
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post #22 of 45 (permalink) Old 10-12-2020, 01:31 PM
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Welcome to TPT.

How about getting something like a 10+ gallon container, putting a clamp-on fine filter sock on it, and then siphoning the bottom regularly. You could then put the water back in using a powerhead and hose. This might be a "middle ground" approach to save water while getting the chunks out before they can break down. You could top off using the solar still water. I use Pothos and Anthurium to dangle in my tank. They grow well and soak up excess nutrients. They also look cool and your Oscar will not dig them up!

The other thing is to just try not doing changes while monitoring water parameters, algal growth and livestock health. Experiment.

BTW. I see your post as a very reasonable question by someone who probably knows more about plant science than most here but is looking for experience based practical input.

Good luck. Please report back and post a couple of photos.
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post #23 of 45 (permalink) Old 10-12-2020, 10:08 PM
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so my theory is if i have my desired params of X Y Z on Sunday with a TDS of A then my water change in week needs to return TDS to A while also topping/reducing any of the other params that may have drifted to get them back to the same values of X Y Z. That needing 5% or 50% is going to depend on the degree of drift of the TDS and other tracked params between changes but when the tracked params (ph, kh gh and nitrates in my case) are constant week after week post water change and so is the TDS then I am (I think) removing as much pollutant as is being added between those changes.
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post #24 of 45 (permalink) Old 10-13-2020, 02:14 AM
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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.




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.
Thanks for that explanation. Also it's good to keep in mind as I plan on moving out your way hopefully within a year's time. I feel like it should really be described as escaping rather than moving, but this isn't the forum for that. lol

What about a whole-house RO/water purification system? Would that be unrealistic?


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post #25 of 45 (permalink) Old 10-13-2020, 05:09 AM Thread Starter
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Thanks for that explanation. Also it's good to keep in mind as I plan on moving out your way hopefully within a year's time. I feel like it should really be described as escaping rather than moving, but this isn't the forum for that. lol

What about a whole-house RO/water purification system? Would that be unrealistic?
Well, it would probably multiply household consumption 2-5 fold, which- considering the cost of water as a fraction of my bill- would be wasteful, but not terribly expensive. For now, I'm making do with an under-the-sink 50 GPD, and one wall-mounted unit outside that is probably closer to 25.

Even then, I'm pretty sure septic treatment out here uses industrial RO to purify the waste water for non-potable re-use, including irrigation and even large ponds (look up the Gilbert Riparian Preserve- I'm almost certain that's entirely re-use water). So that reject water just goes back into circulation.

Locally, folks seem split about RO versus tap for their freshwater aquaria. For small aquaria and for breeders, it's probably more popular.

Send me a message if you're looking for location advice within Phoenix. The city's growing fast (and water consumption is actually lower than it's been since the 1950s). We're better off than, say, Las Vegas and Albuquerque; the impoundments up and down the Salt afford a fantastic buffer for surface water, although I admit the long-term forecast is pretty bleak. Even then, most of our water use in this state goes to agriculture: farming the desert.
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post #26 of 45 (permalink) Old 10-13-2020, 01:16 PM
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Since we’re collecting opinions, I’m not sure there is as much value in w/c’s as I came to believe about ten years ago when I started doing 50% weekly. Prior to that, it was, at most, 20% monthly (before TDS meters), but in a low-tech tank. In both cases, I never (none that I recall) had fish problems, but I attribute this mainly to a level one UVS, strict acclimation protocol and minimization of other known stress inducers. In our aggressively planted high-tech tanks I would think that w/c’s are even less critical given the plants filtering abilities, provided that we monitor nutrient accumulation. So, several months ago, I started 50% w/c’s twice a month and have seen no negative effect, including no algae appearance. I intend to push this further …cautiously.

The PPS system suggests that frequent w/c’s are unnecessary so long as TDS indicates stability, as does Diana Walstad (as mentioned, above). Many of us mention the value of w/c’s, but perhaps these are due to a lack of stability in some area (usually nutrient accumulation). Certainly, there is value if a crisis develops. I do think that frequent w/c’s provide a bigger cushion against the unexpected, much like active substrates do, and are particularly advisable for the inexperienced for this reason.

We know, pretty well, those typical things that kill fish and plants and can measure them, but I’m not sure that other things from the waste stream are harmful long term. I’ve not seen any studies that would definitely affirm this. There are many anecdotes about this, such as “When I don’t do a w/c every week, algae explodes and fish start swimming upside down” or “I haven’t performed a w/c in 20 years and flora and fauna are thriving” so, like much in this hobby, I suspect that each tank has it’s own w/c optimum.

However, even though we may greatly vary on w/c frequency and quantity, I do believe it very important to clean filters frequently (I do so every other week - and it shows the need to do this).
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post #27 of 45 (permalink) Old 10-13-2020, 08:22 PM
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The larger WC changes in fertilizer reset regimes like PPS, EI etc. aren't as arbitrary as they would appear.

If you do not directly measure your plants uptake or the loss of your fertilizer(oxidation, precipitation etc.) directly which is difficult you want to be constantly adding more of fresh fertilizer and removing unused fertilizer and waste.

If you change 50% of your water weekly the accumulation of fertilizer accumulates up to 2X your weekly dosage.
Change only 25% the accumulation up to 4X your weekly dosage.
Change only 10% and the accumulation is eventually 10X your weekly dosage

Now if your net uptake is close to what you are dosing, your plants are healthy and your TDS isn't accumulating a large amount with smaller water changes that changes the conversation.

It is the same with waste products, assuming fish waste production is constant the primaty products organics(not easy to test for), nitrogen, phosphorus are constant the same can be said for waste.

Change 50% and you have 2X the weekly net waste production
25% 4X weekly net waste production
10% 10X weekly net waste production

There are husbandry techniques like water vaccuuming the substrate through a second filter with filter pads and Purigen, that would get rid of Detritus and help with organics and mulm removal, returning the filtered water back to the tank, but even then evaporation and TDS creep will still necessitate topping off the tank with distilled/RO water and still accumulation necessitates some water changes. But if all you have is a 2inch oscar(???) in a 120G there shouldn't be a lot of waste or feeding until it grows up. I assume your oscar and plants aren't already living in semi brackish water already (1000 TDS?).

You can monitor accumulation without monitoring for all compounds if you see significant TDS accumulation its time to do larger water changes. A TDS meter won't measure organics or neutral compounds but assume the ions act as a proxy for everythingelse and they can be your rough guide.


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Last edited by cl3537; 10-13-2020 at 09:37 PM. Reason: 2 inch oscar in a 120G tank!
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post #28 of 45 (permalink) Old 10-13-2020, 09:09 PM
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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.
TDS of your tank water is 1000 or your source water? (Also what is the range of your TDS meter as a lot of the hobbyist ones can't go past 1000).


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Last edited by cl3537; 10-13-2020 at 09:47 PM. Reason: ...
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post #29 of 45 (permalink) Old 10-13-2020, 09:10 PM
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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.
To be clear my understanding was that you were wondering what was in the water that would make someone want to do water changes, so that is what I was addressing. I think it's totally possible to do no-water change tanks because you are still exporting things that could raise TDS via cleaning the filter, trimming plants, etc. The folks at Ocean Aquarium in San Francisco claim to never do water changes over 20 years-- the only water that leaves the tank is from from catching fish, plus they have deep substrate beds (for complete breakdown of mulm) and very heavily planted tanks.

I have enjoyed this topic, and learned a thing or two. Thanks for bringing it up!


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post #30 of 45 (permalink) Old 10-13-2020, 10:12 PM
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The list of "organics" is plentiful. There are amino acids of various types, proteins, glycoproteins, sugars, and others. Anything with carbon and hydrogen is an organic (except bicarbonate and carbonic acid).

Assuming that the many known and unknown "organics" are bad may be wrong. Many of these may be useful in providing energy sources for various life forms in our tanks (bacteria being just one example). Organic molecules are important to the formation of CaCO3 in many organisms. "Organics" can bind with the metals in our tanks, acting as chelators (think: humic/fulvic acids), and may make them easier to consume and simultaneously reduce toxicity.

So, before trying to reduce the many "organics" whose processes we do not fully understand, we may want to be careful about what we ask for, as we may not like what we get in doing it. Unfortunately, these multitudes of "organics", and their impact, simply have not been studied well in aquariums. There is good and bad to all of this, but is the balance a neutral effect? If so, there is no need to worry about them accumulating, if the known dangerous/undesirable results of the organic processes are controlled.
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