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



## Epiphyte (23 Nov 2022)

I've had this nagging question in the back of my mind for some time now, I'm hoping the combined wisdom of UKAPS may help me make better sense of it.

Convention says that with a high tech aquascape, I must perform a 50% water change weekly, which I do, give or take a day or so. My question is though... why?

If I look at my tank, it's roughly 160 litres of RO water (Oase 90P), remineralised to a TDS of 120. It has large amounts of plants, mostly fast growing stem type. Fish stocking for the aquarium size would probably be classified as low, roughly 30 small tetras, a dwarf gourami pair and a flotilla of Red Cherries. I lean dose APT Complete and the whole thing gets turned over with an Oase Biomaster Thermo 600, filled up with excess amounts of Seachem Matrix. None of my hardscape choices affect water quality or chemistry either. For all intents and purposes, the water is immaculate and, minus a small amount of BBA on the hardscape, is completely algae free.

So why with a well maintained and mature aquarium, with plants exporting so many of the nutrients and so little coming from waste, do we do this unusually large water change? If I get to the 7 day mark, everything bad reads zero and nitrates are low, what am I actually exporting via the water change?

I'm not expecting there to be double blind peer reviewed studies over this, but anyone I have ever asked sort of shrugs and says they aren't sure why we really do it. Are we doing it because it's convention? Because there is something in the water we don't traditionally measure that we're exporting? Or am I just pouring perfectly fine water down the sink every week?

I appreciate that when something is going wrong, a big water change is the first thing to do, but this is all assuming a well operating tank.

Interested to hear peoples thoughts.


----------



## Ajm200 (23 Nov 2022)

If you look back at some of the older Estimative Index posts you should find your answer.  There’s lots of scientific talk that explains it properly

When I first joined the forum I was just starting in the hobby.  The advice was to overdose fertiliser to ensure that there was enough of everything, lots of flow and lots of CO2 then a 50% water change at the weekend.

The result for me was a rapidly growing tank with plants that needed lots of maintenance, algae problems and sometimes gasping fish as I didn’t have the experience to balance a tank like that.

I went very low tech.  Some of my tanks are only filtered with plants above and below the water.  I have dirt with a gravel cap, low light, no filter, lots of plants and a few fish.  I add a ferts if the floating plants look like they need it.  The water gets topped up and changed if it is looking a bit yellow.    It’s a little ecosystem I can balance as I’ve removed most of the human factors.   I have no visible algae but had a daphnia population explosion that had to be brought under control


----------



## MichaelJ (23 Nov 2022)

Hi @Epiphyte, Ok, I'll take a stab at this first... Im running low-tech tanks and NEVER did CO2, so keep that in mind.  First off, we do water changes to get rid of waste from fish, uneaten food, plants, algae spores and pathogens etc.. H2O is H2O... if we didn't have any unwanted by-products we could more or less just top off evaporated water and replenish fertilizers thats been eaten by the plants. Now, if your tank is mature (which it is as you state) and have found a balance and is seemingly stable you might _possibly_  be able to get away with less frequent water changes or less amount.  A good approach might be to see what sort of drift you measure in terms of TDS (not everything will show as TDS, but a lot of by-products will). If you remineralize to 120 ppm and see no large drift between water changes it might   suggest that waste creation is roughly cancelled  by uptake... You still want to get rid of that waste though. One suggestion would be to lean on some measurement such as TDS and use your eyes and good common sense - we can usually tell from the _spirit of the plants and livestock_ if we are falling behind on maintenance. The fact of the matter is that WC frequency and amount is not cut in stone - its super tank-depended on specifics such as stocking level vs. plant density etc. Speaking from my own experience I went from 50-60% weekly to 35% every other week (I try to keep it 12 days in-between but it often end up being 14-15 days) and see no difference - if I go really long, like 5 weeks that I had to do over the late spring this year it definitely shows in a bad way - big spike in TDS, some lackluster plant appearance, visible detritus buildup ... For new tanks regardless of tech the consensus around here is generally to suggest at least 50% weekly - more for high metabolism tanks - but again, as the tank matures and plants grow in you_ might_ be able to tweak that to far less.

Cheers,
Michael


----------



## Yugang (23 Nov 2022)

Epiphyte said:


> all assuming a well operating tank


In this case only (partial) EI dosing (or other overdosing) needs big weekly water change. This is because the reset is an essential part of EI to work without poisoning plant and lifestock with the excess amounts of ferts (accumulation).



Epiphyte said:


> Convention says that with a high tech aquascape, I must perform a 50% water change weekly


So this is not true, even not for high tech. If ferts dosing is low, and healthy tank, less water change can work fine


----------



## MichaelJ (24 Nov 2022)

Yugang said:


> In this case only (partial) EI dosing (or other overdosing) needs big weekly water change. This is because the reset is an essential part of EI to work without poisoning plant and lifestock with the excess amounts of ferts (accumulation).



Hi @Yugang, True. However, I never understood the rationale behind this _reset-_ part of the Estimative Index approach as it doesn't make much - if any - mathematical sense. No matter what amounts of fertilizer you are dosing (within reason), you will always reach some sort of equilibrium (where there is no additional accumulation) with your dosing and a sensible WC regime - and if your following EI you are already buying into an approach that is less concerned about "overdosing" 

Cheers,
Michael


----------



## Yugang (24 Nov 2022)

MichaelJ said:


> it doesn't make much - if any - mathematical sense


Actually it does, you can play with the nutrient accumulator to simulate
Nutrient Accumulation Calculator​
Just to clarify the idea, let's take two extreme examples. 

No plants and no water change. After a couple of years the ferts concentrations in the tank will approach the concentrations of the dosing stock solution. 
100% water change weekly. We know after each water change and dosing exactly the ppm in the tank and it will be same every week. This is what EI aims to achieve.

The basic idea of EI is that we don't know how much the plants consume, and therefore we don't know how much ferts we would have to add to keep the tank ppm constant. With a 50% water change reset, the accumulation can never exceed a factor of two above the target for the tank - irrespective of the plant consumption. As we now have limited our maximum accumulation to this factor of 2, we can safely overdose (dose more than plants need). This overdosing is the idea behind EI, so that we can rule out deficiencies.


----------



## GreggZ (24 Nov 2022)

Don't change your water for a couple of months and see how it goes. That's a great way to learn.

Water changes are easily the best thing you can do for your planted tank. If you really want to whip it into shape do a couple of week for a few weeks.

It has more to do with removing organics than anything else. An uber clean tank makes every single other thing easier. No question about that.


----------



## Yugang (24 Nov 2022)

GreggZ said:


> Don't change your water for a couple of months and see how it goes. That's a great way to learn.
> 
> Water changes are easily the best thing you can do for your planted tank. If you really want to whip it into shape do a couple of week for a few weeks.


This



GreggZ said:


> It has more to do with removing organics than anything else.


The point you make for removing organics is clear, but for an EI dosed tank the accumulation of ferts (no waterchange, while continuing to dose) seems an even bigger issue than organics. Of course risks are less when the EI doing has been carefully reduced, and one would hope that we are closer to a balance between dosing and plant consumption.


----------



## Epiphyte (24 Nov 2022)

Lots of interesting reading so far, I'm certainly not looking to avoid water changes for months, I'm just conscious on waste water and wasted time. I completely understand with EI you're doing it to avoid "saturating" the water column with ferts over time. However, is this still the case with lean dosing?

Absolutely understand the idea to clean organics out of the tank, but I could definitely do a good vacuum of the plants and substrates with maybe 1-2 25L buckets.


----------



## KirstyF (24 Nov 2022)

I think the amount of organics being released in a perfectly healthy high tech tank with a few fishes might still be more than most think! and cleanliness is next to…awesomeness!

There is however (like with most things) a range.

The guys who remove every aquasoil bobble and polish it….at least I’m sure that’s the only way they can get tanks THAT clean. (you know who you are. 😉)

And those who merrily trot along on less W/C volumes or frequencies and have very happy tanks.

But, conventional wisdom is conventional for a reason. It covers all bases, should be more than enough to keep most tanks ticking along nicely and certainly isn’t going to do any harm (mostly, quite the opposite) 

Can you do it differently, sure you can. You would need to consider ferts accumulation else your lean APT might not be so lean after a while, and you’d need to figure out what levels worked for your tank in your situation through experimenting…..be prepared for the odd nasty surprise to pop up cos things can happen fast in a high tech! (where did all that algae come from 😱) …..and observe the tank super closely so that it can tell you how you’re doing. 

If all that sounds like fun then go for it.
If the desire to reduce is pressing (time pressure, wanting to reduce water water from RO etc) then consider it.
If you you want to keep it simple….50% WC will do that for you. 😊


----------



## Aqua sobriquet (24 Nov 2022)

Gosh. My two Nano’s get 10% a week ~ if I remember! 😆


----------



## tam (24 Nov 2022)

The 50% and maintaining an equilibrium with the estimative index makes sense, but seven days is also quite an arbitrary number - probably picked because a lot of people water change on the same day of the week. I imagine, you probably wouldn't see a difference if you water changed every 10 days instead, which would save you 16 water changes a year. At which point, I'd start wondering if every two weeks would suffice if your plant growth and numbers looked fine.  

But, I also don't do high tech, so I'm more of a 20% every few weeks.


----------



## LMuhlen (24 Nov 2022)

Another positive influence of this general rule of changing 50% water weekly is to help destroy an old lasting myth that excess water change is bad, that we shouldn't change more than 10% to avoid hurting the balance of the system. I'm not sure how widespread this myth is over there, but I do hear it from time to time, and having it as a general rule to change at least 50% water on tanks is a great way of showing to these people that they shouldn't be afraid to change water.

The way I see it, general rules are meant to provide enough safety margin to prevent as many issues as possible for the widest audience possible. But if you want to optimize your system and are willing to experiment a bit, there is nothing wrong with finding what works for you. However, some of the issues with reduced water changes may be subtle and not immediate, so it is important to keep a sharp eye to avoid having your tank slowly deteriorate in an unnoticed way.


----------



## GreggZ (24 Nov 2022)

Yugang said:


> The point you make for removing organics is clear, but for an EI dosed tank the accumulation of ferts (no waterchange, while continuing to dose) seems an even bigger issue than organics. Of course risks are less when the EI doing has been carefully reduced, and one would hope that we are closer to a balance between dosing and plant consumption.


Yes this important as well. But it's often misunderstood. Folks need to understand how water changes frequency/amount affect water column levels of nutrients.

There is a formula to calculate the theoretical maximum accumulation of nutrients. It's the dosing between water changes divided by the water change percentage.

So let's say someone doses 15 NO3 between water changes. That can mean a lot of things depending on the water percentage.

For instance:

15 ppm NO3 with 25% water change: 15/0.25 = 60 ppm max accumulation
15 ppm NO3 with 50% water change: 15/0.50 = 30 ppm max accumulation
15 ppm NO3 with 75% water change: 15/0.25 = 20 ppm max accumulation

Same dosing, same tank, just different water change percentage. If folks don't understand maximum accumulation they should. In the end we are trying to maintain a steady level of nutrients in the water column.


----------



## hypnogogia (24 Nov 2022)

GreggZ said:


> 15 ppm NO3 with 25% water change: 15/0.25 = 60 ppm max accumulation
> 15 ppm NO3 with 25% water change: 15/0.50 = 30 ppm max accumulation
> 15 ppm NO3 with 25% water change: 15/0.25 = 20 ppm max accumulation


shouldn't that be:
15 ppm NO3 with 25% water change: 15/0.25 = 60 ppm max accumulation
15 ppm NO3 with 50% water change: 15/0.50 = 30 ppm max accumulation
15 ppm NO3 with 75% water change: 15/0.75 = 20 ppm max accumulation


----------



## MichaelJ (24 Nov 2022)

GreggZ said:


> It has more to do with removing organics than anything else. An uber clean tank makes every single other thing easier. No question about that


@GreggZ that is uber true  It's just that what it takes to maintain that_ uber cleanness_ vary by the overall metabolism ( organic waste generation) of our tanks. For instance, my tanks can easily get by with 35% every two weeks (I try to keep it 11-12 days in-between) and they are very clean as far as I can tell.  Someone else may need 60-75% per week to maintain the same level of cleanness... So thats that.

I guess my dosing approach is slightly _out of tune_ with what people are _normally_ doing as I add all my ferts (NPK/Ca/Mg) except for traces, to my WC water (targeted relative to the WC amount only), as opposed to dosing throughout the period in-between WCs.  It just makes the whole thing so much easier and consistent for me.



Epiphyte said:


> I'm just conscious on waste water and wasted time.


Me too and thats why I slowly went from doing +50% weekly to 35% every 11-12 days....



Epiphyte said:


> I completely understand with EI you're doing it to avoid "saturating" the water column with ferts over time. However, is this still the case with lean dosing?


I guess it depends on how you apply your dosing... I am rather lean with my dosing as well and do not have any noteworthy accumulation.



KirstyF said:


> There is however (like with most things) a range.


Very much agree!



tam said:


> but seven days is also quite an arbitrary number


Blame it on the Babylonians - possibly!


LMuhlen said:


> that we shouldn't change more than 10% to avoid hurting the balance of the system


Yes, that is generally considered an _old wife's tale_... However, I can imagine scenarios where the parameters of the water added would vary wildly from the tank water parameters and cause instability (stress on the livestock in particular).  As long as we avoid that, large water changes wont cause problems.

Cheers,
Michael


----------



## GreggZ (24 Nov 2022)

hypnogogia said:


> shouldn't that be:
> 15 ppm NO3 with 25% water change: 15/0.25 = 60 ppm max accumulation
> 15 ppm NO3 with 50% water change: 15/0.50 = 30 ppm max accumulation
> 15 ppm NO3 with 75% water change: 15/0.75 = 20 ppm max accumulation


Good eye I changed it above pressed submit too quick!!!!


----------



## Tim Harrison (24 Nov 2022)

There's these ancient threads too with Tom Barrs (@plantbrain) input...






						EI and water changes
					

What is the general consensus of opinion out there regarding the use of the frequent and large water changes employed by eutrophic dosing methods such as EI. Is it to rid the tank of the supposed build up of metabolic waste products of plants, due to elevated rates of photosynthesis, or is it to...



					www.ukaps.org
				









						Why do i need to change the water?
					

I realise that this may sound like a stupid question, but I would like to explore the issue of water changes a bit to try and understand the chemistry of what is happening in my tank.  So, as background, I run a 350litre planted tank (pressurised CO2 with inline difuser, 2 big Eheim filters...



					www.ukaps.org


----------



## KirstyF (24 Nov 2022)

MichaelJ said:


> guess my dosing approach is slightly _out of tune_ with what people are _normally_ doing as I add all my ferts (NPK/Ca/Mg) except for traces, to my WC water (targeted relative to the WC amount only), as opposed to dosing throughout the period in-between WCs. It just makes the whole thing so much easier and consistent for me.



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! 

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? 

Sorry for all the questions but you’ve got my head ticking now! 🤔😂


----------



## Yugang (25 Nov 2022)

GreggZ said:


> Folks need to understand how water changes frequency/amount affect water column levels of nutrients.
> 
> There is a formula to calculate the theoretical maximum accumulation of nutrients. It's the dosing between water changes divided by the water change percentage.





Yugang said:


> you can play with the nutrient accumulator to simulate


----------



## dw1305 (25 Nov 2022)

Hi all, 


KirstyF said:


> Is it this technical or would you just splosh in a bit extra if *it ever looked like it needed it*?


I'm in the <"splosh camp">.


KirstyF said:


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


I'm still in the <"splosh camp">, it <"does away with all the agonising"> and <"nearly all the  calculations">.

cheers Darrel


----------



## KirstyF (25 Nov 2022)

dw1305 said:


> Hi all,
> 
> I'm in the <"splosh camp">.
> 
> ...



I reckon the splosh camp is not at all a bad place to be. Full on duckweed index fan here and figuring out what works based on observation is ultimately the road to success.

I think my high tech would kick my butt using this technique mind (you’d have to be real quick off ur feet with your obs!) The low tech, however, is a much kinder beast. 😊


----------



## dw1305 (25 Nov 2022)

Hi all,


KirstyF said:


> I think my high tech would kick my butt using this technique mind


I think you are right, things happen a lot more quickly high-tech.  That is partially why I like low-tech, it suits <"my fish-keeping approach">.

cheers Darrel


----------



## ceg4048 (25 Nov 2022)

KirstyF said:


> 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?


It's suggested that you review the EI Dosing article in the Tutorial section of the forum. This is what happens when folks make assumptions about a technique that they don't fully understand. In Post #18 Tim Harrison refers to a thread with an identical question. The guy who invented EI responds to the question. The reason for water changes has never changed since day 1 of aquariums. This is an issue of cleanliness. 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.
Water changes have nothing to do with nutrient management. If we were concerned with nutrient management then EI would look much differently, and it would no doubt contain steps to lowere the dosing or to stop the dosing for some period of time to allow the nutrient level to deplete.
So we simply follow the recipe and dose the prescibed amounts of macrontrients as well as micronutrients and then forget the rest. All of that other stuff about nutrient managemen and buildup is complete rubbish. Dirty tanks are problematic, so we clean them using standard procedures. It's also a good idea to clean the dirt that accumulates on the leaves by gently rubbing the leaves etween thumb and fingers. 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. Stop worrying about all these charts and  techno-babble because its all an illusion to blind you from the truth.

Cheers,


----------



## Yugang (26 Nov 2022)

ceg4048 said:


> Water changes have nothing to do with nutrient management.


Strictly speaking this is true, but if you don't do the big water change you would need test kits to know what your water looks like. It is possible, but a lot of work and a lot of money for the limited precision that test kits give.


ceg4048 said:


> So we simply follow the recipe and dose the prescibed amounts of macrontrients as well as micronutrients and then forget the rest. All of that other stuff about nutrient managemen and buildup is complete rubbish.


You can 'forget the rest' _because_ you do the big WC. The beauty of your big water change is that you can go without complicated nutrient ppm testing, and still dose non limiting nutrient without running the risk that you plants and fish swim in a salt bath. So in that sense the big water change keeps your nutrient management simple and with limited risks.



ceg4048 said:


> This is an issue of cleanliness.


True, but cleanliness involves pruning, soil, filter and all general maintenance. I prefer 50% or more WC from my soft HK tap water, so am not advocating less than that. But, going back to OP's original question is 50% really necessary (or could it be less, like 30% for 500 l tank and having to rely on RO water)? I believe one could safely go to perhaps 30%, make sure to dilligently maintain the tank and filter (no full EI with this 3 fold accumulation). As you say, it is never in one ratio, one magic number, so smaller WC % is perhaps not optimal but could be a sensible compromise.


----------



## KirstyF (26 Nov 2022)

ceg4048 said:


> It's suggested that you review the EI Dosing article in the Tutorial section of the forum. This is what happens when folks make assumptions about a technique that they don't fully understand. In Post #18 Tim Harrison refers to a thread with an identical question. The guy who invented EI responds to the question. The reason for water changes has never changed since day 1 of aquariums. This is an issue of cleanliness. 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.
> Water changes have nothing to do with nutrient management. If we were concerned with nutrient management then EI would look much differently, and it would no doubt contain steps to lowere the dosing or to stop the dosing for some period of time to allow the nutrient level to deplete.
> So we simply follow the recipe and dose the prescibed amounts of macrontrients as well as micronutrients and then forget the rest. All of that other stuff about nutrient managemen and buildup is complete rubbish. Dirty tanks are problematic, so we clean them using standard procedures. It's also a good idea to clean the dirt that accumulates on the leaves by gently rubbing the leaves etween thumb and fingers. 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. Stop worrying about all these charts and  techno-babble because its all an illusion to blind you from the truth.
> 
> Cheers,



Hi There
Always good to hear from you. 😊
As my opening gambit to the Op was that cleanliness is next to awesomeness I don’t think our opinions in that area are too dissimilar. 
You might note, however, that the OP has stated that he doses lean and therefore it might be reasonable to assume that ferts accumulation may be of concern to him. Whether or not it may be of concern to others is, IMO, entirely up to them. I don’t choose to judge either way.

He has also expressed a desire to reduce WC quantities for a number of reasons. Production of RO is potentially costly, time consuming and wasteful of water and so considering a regime of less than 50% is not unreasonable, but may have undesirable side effects, and close observation (and remedial action if required) is IMO necessary to ensure the tank doesn’t suffer, as mentioned in my first post. There are plenty of folks that vary somewhat from that 50% and still run very successful tanks but caution and observation is wise advice. Personally I do a 50% weekly WC without fail, but that’s me. 

My queries to Michael are because I have a genuine interest in what he is doing with his tank and how he has chosen to manage his dosing based on lower WC’s at longer intervals.

These things are of personal interest to me and I play with dosing a lot, sometimes to no effect, sometimes with poor results and sometimes with better. I do this because I enjoy it and I enjoy what it teaches me but I don’t prescribe to (or advise) any particular regime, I simply observe my particular tank in my particular circumstance and occasionally share those observations.

You and many others follow the EI ‘recipe’ (as did I when I set out) and have beautiful and successful tanks and I’m all for that. If you are ‘dosing to excess’ with no concerns for accumulation then you are absolutely right, WC’s are purely about maintenance. Others prefer not to have high levels of dosing and WC’s are, in fact, a way of ‘managing’ that. I respect that choice too.

For me, these days I choose to mess with my ferts on a fairly regular basis just to see what happens and I gain pleasure from the learning. Horses for courses right! 😊


----------



## MichaelJ (26 Nov 2022)

KirstyF said:


> 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 



KirstyF said:


> 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 😊)
> 
> ...


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 (27 Nov 2022)

MichaelJ said:


> 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.
> ...



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. 😊


----------



## Tim Harrison (27 Nov 2022)

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 (29 Nov 2022)

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 (29 Nov 2022)

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 (29 Nov 2022)

Hi all,


Malarky said:


> 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">.


Malarky said:


> 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 (29 Nov 2022)

Malarky said:


> 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_ (29 Nov 2022)

Yugang said:


> The basic idea of EI is that we don't know how much the plants consume, and therefore we don't know how much ferts we would have to add to keep the tank ppm constant. With a 50% water change reset, the accumulation can never exceed a factor of two above the target for the tank - irrespective of the plant consumption.


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.


Epiphyte said:


> 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.


LMuhlen said:


> 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.


ceg4048 said:


> 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.


ceg4048 said:


> 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 (30 Nov 2022)

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 (30 Nov 2022)

Hi all, 


PARAGUAY said:


> 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


----------



## Tim Harrison (30 Nov 2022)

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 🙂






						UKAPS Forum Rules and Guidelines
					

The rules did not migrate as they were on a Global Announcement and that did not convert, so here are the UKAPS rules once again for a reminder to old and new members. Cheers.     1. Treat others how you would like to be treated yourself. Remain polite at all times and avoid aggressive styles of...



					www.ukaps.org


----------

