The weekly 50% water change.... why?

[MichaelJ]

Curious about this.
So, if you are adding ferts to WC water at a specified level, we would assume that the water in the tank has been depleted to some extent by uptake, so your starting point moves progressively downwards. Your top up ppm is consistent so doesn’t compensate for that, unless your top up ppm is, in itself, enough for the tank, even if the remaining water were at 0, which would, effectively prevent any potential for an underdose!

Hi @KirstyF,
With this dosing approach I will never exceed my target levels. if the uptake is zero (which is unrealistic obviously) the dosed fertilizer amounts I withdraw with the old water would be exactly the same as I put back in with my fresh WC water. Simple. Since I am only targeting my WC water my water column will always be considerably lower, but high enough so it never become a problem.

Now, the tricky (not that tricky actually) part is to find that balance where what you add compensates for the uptake and you never run dry on any important fertilizers. If I target the 35% WC water at say 4 ppm of N and the uptake is 2 ppm weekly, I would eventually end up being out of - or dangerously low - on N before the next WC.. a bad situation. However, if I guess the uptake being 1.5 ppm/wk I would still have about 1.2 ppm at the end of the WC cycle over time - enough for variation in uptake and eventualities. So I just have to make sure my targets are realistically high enough to cover for the WC cycle. Of course, the only meaningful way I can tell if I am starting to get into trouble is by looking at the health of my plants - floating plants in particular (I am big fan of the duckweed index). If I see deficiencies I just crank up the dosing a bit - That has only happened a couple of times in half a year or so. Easy.

So why am I doing it this way you may ask... well, I only have to remember to dose once with each WC (NPK/Ca/Mg) and its low and slow. I am not inducing any large variations in water parameters - I believe that is good for my live stock and stability of my tanks. My tanks are very clean, I have zero algae, I have healthy plants and I am fairly confident I am not using more fertilizers (or minerals) than I need to - slightly more, but nothing crazy(!) and I am able to keep my TDS low - again, for the benefit of my livestock. Keep in mind I am only running low tech tanks... I have no idea if this would work in a high tech environment - perhaps, perhaps not, given how everything is hysterically accelerated in such an environment. But for me at least, it's been working very well for a long time now and thats all that matters to me. The beauty of this hobby is that many different approaches will work - be it the occasional splosh (@dw1305), EI or meticulous lean (@Happi)... or some hybrid in-between all of this, which is the path that I think I have chosen 🙂

i.e the amount of ferts in the top up water is adequate for the tank as a whole regardless of uptake.

Is it this technical or would you just splosh in a bit extra if it ever looked like it needed it? (Which can be an equally effective method if you know what to look for 😊)

Also, how do you set ur micro target? Do you pick a total target dose and then simply divide it into however many doses you will be putting in over the WC gap and does this influence the target number you choose or the number of doses, as each individual dose would be smaller, the more doses it is split into.

i.e more smaller doses? or typical 1/3 dose but more days apart?

Also, if the micro target was a total based on full water volume and not just WC water, would that then not accumulate?

For micros I just target the whole tank and split it into two doses; one several hours to a day after the WC and one mid-cycle (6 days after but I often skip that). Yes, micros could potentially accumulate, but I am not sure how big of a deal that is with my small dosing relatively to the dense plant mass and I often skip the mid cycle dose (because I forget 🙂 ), so I don't think its an issue, but it's certainly something I am aware of.

Cheers,
Michael

 

[KirstyF]

Hi @KirstyF,
With this dosing approach I will never exceed my target levels. if the uptake is zero (which is unrealistic obviously) the dosed fertilizer amounts I withdraw with the old water would be exactly the same as I put back in with my fresh WC water. Simple. Since I am only targeting my WC water my water column will always be considerably lower, but high enough so it never become a problem.

Now, the tricky (not that tricky actually) part is to find that balance where what you add compensates for the uptake and you never run dry on any important fertilizers. If I target the 35% WC water at say 4 ppm of N and the uptake is 2 ppm weekly, I would eventually end up being out of - or dangerously low - on N before the next WC.. a bad situation. However, if I guess the uptake being 1.5 ppm/wk I would still have about 1.2 ppm at the end of the WC cycle over time - enough for variation in uptake and eventualities. So I just have to make sure my targets are realistically high enough to cover for the WC cycle. Of course, the only meaningful way I can tell if I am starting to get into trouble is by looking at the health of my plants - floating plants in particular (I am big fan of the duckweed index). If I see deficiencies I just crank up the dosing a bit - That has only happened a couple of times in half a year or so. Easy.

So why am I doing it this way you may ask... well, I only have to remember to dose once with each WC (NPK/Ca/Mg) and its low and slow. I am not inducing any large variations in water parameters - I believe that is good for my live stock and stability of my tanks. My tanks are very clean, I have zero algae, I have healthy plants and I am fairly confident I am not using more fertilizers (or minerals) than I need to - slightly more, but nothing crazy(!) and I am able to keep my TDS low - again, for the benefit of my livestock. Keep in mind I am only running low tech tanks... I have no idea if this would work in a high tech environment - perhaps, perhaps not, given how everything is hysterically accelerated in such an environment. But for me at least, it's been working very well for a long time now and thats all that matters to me. The beauty of this hobby is that many different approaches will work - be it the occasional splosh (@dw1305), EI or meticulous lean (@Happi)... or some hybrid in-between all of this, which is the path that I think I have chosen 🙂


For micros I just target the whole tank and split it into two doses; one several hours to a day after the WC and one mid-cycle (6 days after but I often skip that). Yes, micros could potentially accumulate, but I am not sure how big of a deal that is with my small dosing relatively to the dense plant mass and I often skip the mid cycle dose (because I forget 🙂 ), so I don't think its an issue, but it's certainly something I am aware of.

Cheers,
Michael

Thank you Michael for that comprehensive response 😊

Interesting stuff, particularly regarding those longer gaps between micro doses………..would it work ok in a hard water tank I wonder or perhaps Fe may still be needed at greater frequency 🤔 but I won’t hijack the Ops thread any more so I’ll cogitate and raise an appropriate thread or PM. 😊

 

[Guest]

This maybe of interest. It’s not a million miles away from what @MichaelJ is suggesting and it’s still relevant to the op, albeit regarding water changes in low-energy planted tanks.

Non Co2 Methods

Non co2 methods for planted tanks

barrreport.com

 

[Epiphyte]

Lots of interesting reading in this thread, thank you all for your contributions!

I've swapped from changing 80-ish litres down to 50 this week, seeing no immediate detriment to the tank, I'll keep it up for the next few weeks and see if anything interesting happens, though I suspect it won't on a mature and stable tank.

As always, especially in this hobby, there are many ways to skin the preverbal cat, but great to hear how others do it and their reasons.

 

[Malarky]

I'm midway through reading Diana Louise Walstad's 'Ecology of the Planted Aquarium: A Practical Manual and Scientific Treatise', I'm fairly new to the hobby and finidng this book revelatory in terms of how to view the dynamics of aquarium chemistry. I think it's pertinent to this and probably most of the threads on here, I can't recommend it highly enough. It's out of print and expensive secondhand but reasonably priced on Kindle.

 

[dw1305]

Hi all,

Diana Louise Walstad's 'Ecology of the Planted Aquarium: A Practical Manual and Scientific Treatise',

She gets <"a frequent mention"> and if I only owned one book on Aquariums, it would be hers.

After <"Ecology of the Planted Aquarium"> was published she had a bit of a revision with regard to water movement and water changes <"Walstad revises">.

It's out of print and expensive secondhand

It is a shame, but you might be interested in <"Sandy Nook . . ."> and if you still have some money left? There are always the works of Takashi Amano <"Nature Aquarium World Takashi Amano">.



cheers Darrel

 

[MichaelJ]

It's out of print and expensive secondhand but reasonably priced on Kindle

It's readily available on Amazon US. I like this book a lot. That said, some of the practical advice given (in particular p182-185) especially with regards to maintenance is problematic in my opinion. There is a somewhat implied reliance on waste to feed the plants which to me sounds exceedingly hard to manage. Personally, I don't even factor in waste into my dosing regime and hope to get rid of enough water-column borne fish- and food waste with my moderately frequent water changes and filter cleanings. I wish they would put out a new edition with the revised takes on water movement and water changes. Anyway, the book is highly recommended despite its shortcomings.

Cheers,
Michael

 

[_Maq_]

I think this assumption is less than fully correct. Some nutrients tend to get bound in poorly soluble compounds and/or live/dead matter. With WC you remove only smaller part of them, and accumulation of some nutrients - phosphorus and all micros - is inevitable.
I suspect that some tanks run into trouble after several years of success exactly due to accumulation of micronutrients.

Absolutely understand the idea to clean organics out of the tank, but I could definitely do a good vacuum of the plants and substrates

Significant part of organics is dissolved within the water column.

general rule of changing 50% water weekly is to help destroy an old lasting myth that excess water change is bad

I think it's not that simple. Excess water change can be pretty harmful IF performed after prolonged period of low or missing water changes.
It all goes down to stability and adaptation. If your tank inhabitants are adapted to large and regular WC, you are at risk whenever you you take a break. And vice versa, if your tank is adapted to low WC, excess WC may be a shock.

Plants being fed high doses of nutrition produce large amounts of organic waste, much of it in the form of complex carbohydrates, which attract the attention of aerobic micro-organisms. As we know, these microbes consume vast amounts of oxygen and this will inevitable lead to a decline in fish and plant health.

Not sure whether we can call it organic "waste", and that "complex carbohydrates" deserve mention it this context. Organic compounds of all sorts are exuded and attract microbes.
It makes little difference whether these microbes decompose organic compounds aerobically or anaerobically. Anaerobic processes are just a sort of detour - resulting compounds are half-products which have to be oxidized in the end, anyway.
Therefore, we can save expert language and say in simple terms: Any organic pollution means decrease of available oxygen thanks to biological oxygen demand.

The dirt being excreted by the plants accumulate to such an extent that it actually causes a barrier against which nutrients and especially CO2 find difficult to penetrate.

Plants do not exude "dirt" which would harm leaves' access to gasses & nutrients. Quite the contrary, plants exude compounds repelling bacteria, fungi and algae from their leaves, and that is why healthy plants' leaves are (almost) clean.
However, plants do exude organic compounds which are attractive for bacteria, bacteria create biofilms on leaves' surface, and fungi & algae follow IF conditions for plants are in any way less than satisfactory.
Such conditions may be given namely by excess of organics => excess of microbes in the water column. To prevent it, we apply water changes and activated carbon.

 

[PARAGUAY]

I try to not overcomplicate the benefits of water changes ,amounts worked out by the aquarist eg Josh Sim 20% a week on a CO2 set up or say George Farmer 50% on his CO2 tanks. Then on non CO2 set ups @dw1305 eg regular 10% changes. We do them for plant growth ,plants produce waste when in growth and also fish produce waste. I think it's less to do with nutrients and more to do with removing waste. Many times l have for any reason my neglected tanks (no w/c for weeks)with huge w/c say over 50% nothing ever detrementral to fish or tank

 

[dw1305]

Hi all,

Then on non CO2 set ups @dw1305 eg regular 10% changes. We do them for plant growth ,plants produce waste when in growth and also fish produce waste.
I think it's less to do with nutrients and more to do with removing waste. Many times l have for any reason my neglected tanks (no w/c for weeks)with huge w/c say over 50% nothing ever detrementral to fish or tank

I do, a <"6 pint milk carton of rainwater for nano-tanks"> and <"two cartons for ~70 litre tanks">, if I've been away from home / work for a couple of weeks I just <"change a bit more water"> when I'm back.

cheers Darrel

 

[Guest]

I agree @PARAGUAY we’re perhaps overthinking the whole water changes thing. Whatever works for you in your unique circumstances; there is more than one route to success.

It’s been said here many times before, but 50% water change is just a guide or starting point. One of a handful of ideas, along with EI, 10x flow etc, that are designed to simplify the hobby and increase the chances of success, especially for those just starting out.

And the evidence shows it works. We could argue the toss over why all day long. But it doesn’t really matter 🙂

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