Nutrient upper bounds? Reducing EI water changes without encountering toxicity. - The Planted Tank Forum
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post #1 of 14 (permalink) Old 01-16-2020, 12:59 AM Thread Starter
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Nutrient upper bounds? Reducing EI water changes without encountering toxicity.

I'm planning on fertilizing my tank according to EI, but I can't do weekly water changes; I'm shooting for bi-weekly. As you probably know, the driving factor behind EI water changes is the maximum allowable concentration of each nutrient. Interestingly, I've been unable to find much discussion on peak concentrations before toxicity/reduced growth is encountered.

It's remarkably easy to calculate the maximum concentration a nutrient will reach assuming no uptake. It's just a geometric infinite series, which gives the formula:


  • C = A/B, where C is the peak concentration, A is the amount of nutrient added between water changes, and B is the proportion of water changed.


So, if I added 5ppm of KNO3 twice a week, and I went two weeks between 50% water changes, the maximum concentration of K would be 5󫎾/0.5 = 40 ppm. Or, you could just use Rotala Butterfly's nutrient accumulation calculator, but this is so easy especially with 50% water changes. Of course, any plant uptake will reduce concentrations below what this calculates, but this is the conservative case.


The question is: what are these maximum values before either stuff starts to die or plants stop growing? I've done a bunch of research, and here's the best I've been able to find.


Do you guys have sources or experience that contradict any of these values?

Based on NilocG's recommended doses for EI + CSM+B + GH Booster, the five nutrients that will reach undesired levels first are:
  1. Phosphate: limit is 0.8 the weekly dose; however, remember it is not toxic until about 50 this ideal maximum level
  2. Nitrate: limit is 3.6 the weekly dose
  3. Manganese: limit is 4.1 the weekly dose
  4. Zinc: limit is 4.7 the weekly dose
  5. Copper: limit is 7.8 the weekly dose
Remaining nutrients range from 16 the weekly dose (iron) to 30,300 the weekly dose (molybdenum).

According to this, dosing at NilocG's recommendations with a biweekly 50% water change would put peak Mn and NO3 levels at 1.1 the limit, and PO4 would be 5 the limit. Of course, there will be nutrient uptake by plants, and even a small amount would keep Mn and NO3 safe. I might get some algae from the PO4, but we'll see.


I'd love to hear your thoughts - let me know if this info/logic isn't right. Primarily, I'm interested in verification or corrections on maximum levels for nutrients: both the maximum value before growth is impaired and the maximum value before toxicity occurs (in plants, fish, shrimp, snails, etc.). Hopefully this can help some people!
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post #2 of 14 (permalink) Old 01-16-2020, 01:34 AM
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[*] PO4 - ~2 ppm (equivalent to 0.65 ppm phosphorous): Non-toxic at levels at 100 ppm or higher, but algae growth is reported to be an issue at levels as low as 2 ppm. Some people report going much higher than 2 ppm without issue. S - 100+ ppm: [/URL]
IMO you are making this WAY more complicated than it needs to be.

Let's just take the PO4 reference above. The notion that high PO4 causes algae has been disproved over and over again, and is more like folklore at this point. Just saying myself (and may others) dose enough PO4 that would make your head spin.

If you really want help with dosing, I would start a journal and list all of the parameters of your tank. It's nearly impossible for anyone to make any useful suggestions without knowing more about the tank. Is this going to be a high light tank packed full of stems......medium light with easier plants.....low light with slow growers? Makes a big impact on dosing strategy.

And keep in mind fine tuning dosing is only part of the equation. Getting light, CO2, and maintenance right for your tank goals are equally as important.

As to biweekly water 50% changes, you are correct the basics would be max accumulation at 4 times weekly dosing. But that does not take into account plant mass/uptake and any fish load. No one can tell you right now what levels might end up being toxic. And if really want to get deep into the weeds, look up Mulder's chart and you will see that toxicity symptoms could also be relative to your particular levels of every nutrient and their relationship to each other.

So whatever you do, trust me it will take trial and error to get it right, and you aren't going to find those answers by searching the net.

Good luck and look forward to learning more about what you are up to.


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Last edited by Greggz; 01-16-2020 at 03:19 AM. Reason: typo
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post #3 of 14 (permalink) Old 01-16-2020, 06:08 AM
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I personally dose my macros once a week. My micro targets are Fe0.1ppm, Mn,0.05, B 0.02, Zn0.02, Cu 0.01 and Mo and Ni at 0.001. Note my tank is a medium light RO water with inert substrate. I have only had one micro become deficient Mn but I don't know why. I have seen nickel in the ICP-OES test at 0.1ppm with no obviuosue advert effects.

n a small 1 gallon plant only tank I have dosed Fe0.5, Mn0.25, B, 0.1, Zn 0.1, cu 0.5 and seen no adverse effects on the plants. Basically I put in the 1 gallon plant only tank a dose adequate for a 5 gallon tank.

As to Cu I have personally not seen any adverse effects at 0.02ppm on invertebrates. Furthermore most people are worried about copper in the fertilizer when most of the copper in aquariums comes from copper pipes the tap water flows through. Also keep in mind copper is essential for plants and shrimp. Both would die without it. I Think that if we measured Cu levels a lot of shrimp tanks we would find many with Cu valves well above the 0.02 limit you referenced. THE EPA limits copper in water to a maximum of 1.3ppm.
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post #4 of 14 (permalink) Old 01-16-2020, 03:12 PM
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... My micro targets are Fe0.1ppm, Mn,0.05, B 0.02, Zn0.02, Cu 0.01 and Mo and Ni at 0.001. Note my tank is a medium light RO water with inert substrate.
Hey surf, can you please share a pic of your tank with those parameters?
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post #5 of 14 (permalink) Old 01-16-2020, 06:40 PM Thread Starter
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IMO you are making this WAY more complicated than it needs to be.

Let's just take the PO4 reference above. The notion that high PO4 causes algae has been disproved over and over again, and is more like folklore at this point. Just saying myself (and may others) dose enough PO4 that would make your head spin.

If you really want help with dosing, I would start a journal and list all of the parameters of your tank. It's nearly impossible for anyone to make any useful suggestions without knowing more about the tank. Is this going to be a high light tank packed full of stems......medium light with easier plants.....low light with slow growers? Makes a big impact on dosing strategy.

And keep in mind fine tuning dosing is only part of the equation. Getting light, CO2, and maintenance right for your tank goals are equally as important.

As to biweekly water 50% changes, you are correct the basics would be max accumulation at 4 times weekly dosing. But that does not take into account plant mass/uptake and any fish load. No one can tell you right now what levels might end up being toxic. And if really want to get deep into the weeds, look up Mulder's chart and you will see that toxicity symptoms could also be relative to your particular levels of every nutrient and their relationship to each other.

So whatever you do, trust me it will take trial and error to get it right, and you aren't going to find those answers by searching the net.

Good luck and look forward to learning more about what you are up to.

Greg, thanks for the info. What can I say? I'm an engineer, overcomplicating things is what I do!
Do you have any idea what your PO4 concentration is? Dosing a ton doesn't necessarily mean there is a high concentration in the water, and it would help to have a frame of reference.
I realize that achieving ideal plant growth is a complicated process of testing and trial and error - hopefully I'll be able to invest the time to go down that road, but right now I'm just trying to figure out how to keep from killing everything.
Thanks for referring me to Mulder's chart - I was aware of those interactions (e.g. Ca/Mg mentioned in my original post) but didn't know what they all were. And that's a good point on bio-load; I imagine I could estimate what that's contributing based on the breakdown of the food I'm feeding. Probably mostly NO3 and PO4.

I'll keep you updated! I'm about to start a journal for this tank that I'll try to keep updated.


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I personally dose my macros once a week. My micro targets are Fe0.1ppm, Mn,0.05, B 0.02, Zn0.02, Cu 0.01 and Mo and Ni at 0.001. Note my tank is a medium light RO water with inert substrate. I have only had one micro become deficient Mn but I don't know why. I have seen nickel in the ICP-OES test at 0.1ppm with no obviuosue advert effects.

n a small 1 gallon plant only tank I have dosed Fe0.5, Mn0.25, B, 0.1, Zn 0.1, cu 0.5 and seen no adverse effects on the plants. Basically I put in the 1 gallon plant only tank a dose adequate for a 5 gallon tank.

As to Cu I have personally not seen any adverse effects at 0.02ppm on invertebrates. Furthermore most people are worried about copper in the fertilizer when most of the copper in aquariums comes from copper pipes the tap water flows through. Also keep in mind copper is essential for plants and shrimp. Both would die without it. I Think that if we measured Cu levels a lot of shrimp tanks we would find many with Cu valves well above the 0.02 limit you referenced. THE EPA limits copper in water to a maximum of 1.3ppm.

Thanks for your experience. Those nutrient values - are those the amounts you're dosing, or are they the amount you've actually tested at?

That's an interesting point on copper. Does water really gain an appreciable amount of copper from the pipes? Also a good point on EPA copper limits, although I doubt many places are at the limit - my town's water is 0.027ppm. Regardless, I think most water conditioners are supposed to remove copper, right?
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post #6 of 14 (permalink) Old 01-16-2020, 06:54 PM
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This is quite an interesting discussion for me. I'm seeing fairly spectacular improvement by turning off half my lights, changing out 25% of my water daily, and dosing the change water to my targets on all nutrients. It sure seems like the more actively growing plants are depleting some nutrient, but I haven't pinned down which yet; and I'd sure like to not have to change so much water. (Though I suppose it's good weight training.)
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post #7 of 14 (permalink) Old 01-16-2020, 07:05 PM
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The water changes serve a dual function. They not only keep dosed nutrients in range, but they also remove organics that in effect will become nutrients as they breakdown. It's these "nutrients" that you want to deplete as they are triggers for algae and other issues.

My tank for example runs an average of 40-60ppm dosed KNO3 and it's very clean and the fish are very healthy. Tanks without water changes or very little usually rely on extremely heavy plant mass and fairly low stocking.
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post #8 of 14 (permalink) Old 01-16-2020, 10:37 PM
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Greg, thanks for the info. What can I say? I'm an engineer, overcomplicating things is what I do!
Do you have any idea what your PO4 concentration is? Dosing a ton doesn't necessarily mean there is a high concentration in the water, and it would help to have a frame of reference.
I can tell you what I do, but that's not necessarily what I recommend to anyone. What I've done for years is report what I am doing and document with photos so that you can see the results. But that's what happens in MY tank..........inert substrate column fed with high light and loads of stems. What works in yours may be different.

That being said, I pre dose the RO water I use for water changes to NPK 36:14:35. Between plant uptake and fish load NO3 stays pretty constant all week while PO4 drops to somewhere around 8 or so by the end of the week. I very rarely test, and when I do I first test a calibrated solution. I wouldn't base many decisions on test kits without first knowing the readings are correct.

Now as to estimating your NO3 & PO4 from fish load, you can but it is of little value. Personally I completely disregard that and watch the plants very carefully. They will tell you how they like what you doing. When I first got started, I was told there was no need for me to dose NO3/PO4 because of my heavy fish load. Made sense to me....except my plants were starving. I learned to stop dosing based on what I THOUGHT would happen, but rather what I actually see.

In general, getting to toxic levels would take some extreme dosing. Too much of macro nutrients is rarely an issue, unless something is really out of whack. If you would like to learn more about my dosing, I have a link to my tank parameters in my signature. I also have some excel spreadsheets in a google drive that you might find helpful. One is an accumulation worksheet for EI dosing which you might like. If you download it contact me and I will help you go through it.

Now all that gibberish being said, equally important are light levels, CO2 levels and maintenance schedules. As mentioned by @Asteroid above, water changes are not only useful for resetting ferts, but also for removing dissolved organics and keeping the tank uber clean. This is especially true if you have any decent fish load at all. A clean well maintained tank is the single best defense against algae. Personally I change 70% per week and I know both my fish and plants thank me.


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post #9 of 14 (permalink) Old 01-21-2020, 12:05 AM Thread Starter
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I can tell you what I do, but that's not necessarily what I recommend to anyone. What I've done for years is report what I am doing and document with photos so that you can see the results. But that's what happens in MY tank..........inert substrate column fed with high light and loads of stems. What works in yours may be different.

That being said, I pre dose the RO water I use for water changes to NPK 36:14:35. Between plant uptake and fish load NO3 stays pretty constant all week while PO4 drops to somewhere around 8 or so by the end of the week. I very rarely test, and when I do I first test a calibrated solution. I wouldn't base many decisions on test kits without first knowing the readings are correct.

Now as to estimating your NO3 & PO4 from fish load, you can but it is of little value. Personally I completely disregard that and watch the plants very carefully. They will tell you how they like what you doing. When I first got started, I was told there was no need for me to dose NO3/PO4 because of my heavy fish load. Made sense to me....except my plants were starving. I learned to stop dosing based on what I THOUGHT would happen, but rather what I actually see.

In general, getting to toxic levels would take some extreme dosing. Too much of macro nutrients is rarely an issue, unless something is really out of whack. If you would like to learn more about my dosing, I have a link to my tank parameters in my signature. I also have some excel spreadsheets in a google drive that you might find helpful. One is an accumulation worksheet for EI dosing which you might like. If you download it contact me and I will help you go through it.

Now all that gibberish being said, equally important are light levels, CO2 levels and maintenance schedules. As mentioned by @Asteroid above, water changes are not only useful for resetting ferts, but also for removing dissolved organics and keeping the tank uber clean. This is especially true if you have any decent fish load at all. A clean well maintained tank is the single best defense against algae. Personally I change 70% per week and I know both my fish and plants thank me.

Excellent info, thanks Greg!
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post #10 of 14 (permalink) Old 01-21-2020, 12:48 AM
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You will need to dose more than twice or more EI micros to even start getting a whiff of micro tox in my experience. My OPINION is that when you dose non-limiting micros you are inducing gas exchange limitations in your plants which often has a grotesque appearance. Thus, plants tend to look better in our aquaria under low micro dosing as it is difficult to engineer improved gas exchange at the water/plant interface. Increasing the driving force (concentration) can only do so much.
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post #11 of 14 (permalink) Old 01-21-2020, 01:51 AM
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I'd love to hear your thoughts - let me know if this info/logic isn't right.
I can't say if the logic is right or wrong.
But a small bit to add to the thread.

Been measuring plant consumption for almost 2 years.
Using NO3 & Fe as the targets for our mixes the largest NO3 daily consumption has been 3.5ppm and the Fe consumption has never gotten over .015ppm per day.
This is in a heavily planted tank such that finding room for any plant additions is an issue.
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post #12 of 14 (permalink) Old 01-22-2020, 05:02 AM
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Thanks for your experience. Those nutrient values - are those the amounts you're dosing, or are they the amount you've actually tested at?
Those are the amounts I dose to . however I do have lab result that show that most nutrients were close to my target does with the exception of Manganese and nickel. As I stated earlier the lead test did show that I had a deficiency in Manganese. I don't know why that occurred but adding Manganese did correct the problem. Nickel is a bit high, probably do to my cheap scale not being accurate at minimum reading.I use RO DI water so I know the water is not adding anything.

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That's an interesting point on copper. Does water really gain an appreciable amount of copper from the pipes? Also a good point on EPA copper limits, although I doubt many places are at the limit - my town's water is 0.027ppm. Regardless, I think most water conditioners are supposed to remove copper, right?
I don't use tap water in my tank but I did one time test for copper out of cureosity. My tap water has 50ppm of copper in it. As to water conditioners, mater cannot be created or destroyed. So how can adding something to the water remove anything if nothing is removed from the aquarium?

Chlorine is not removed from the water by a water conditioner. It simply react it it with something else like sodium. The result of the reaction is salt that is not hazardous. It doesn't remove chlorine it just converts it to a salt that is not toxic. Now some water conditioners say that they detoxify heavy metal but there is no information available saying how that is done. Sachem does state heavy metals include copper zinc, nickel, and iron. All those metals are needed by plants to grow. If Seachem Prime removed them then it would stand to reason that fertilizer would not work if prime is applied to the water. And yet people are not seeing any effect on fertilizers by seachem prime.
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post #13 of 14 (permalink) Old 01-22-2020, 03:33 PM Thread Starter
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Those are the amounts I dose to . however I do have lab result that show that most nutrients were close to my target does with the exception of Manganese and nickel. As I stated earlier the lead test did show that I had a deficiency in Manganese. I don't know why that occurred but adding Manganese did correct the problem. Nickel is a bit high, probably do to my cheap scale not being accurate at minimum reading.I use RO DI water so I know the water is not adding anything.



I don't use tap water in my tank but I did one time test for copper out of cureosity. My tap water has 50ppm of copper in it. As to water conditioners, mater cannot be created or destroyed. So how can adding something to the water remove anything if nothing is removed from the aquarium?

Chlorine is not removed from the water by a water conditioner. It simply react it it with something else like sodium. The result of the reaction is salt that is not hazardous. It doesn't remove chlorine it just converts it to a salt that is not toxic. Now some water conditioners say that they detoxify heavy metal but there is no information available saying how that is done. Sachem does state heavy metals include copper zinc, nickel, and iron. All those metals are needed by plants to grow. If Seachem Prime removed them then it would stand to reason that fertilizer would not work if prime is applied to the water. And yet people are not seeing any effect on fertilizers by seachem prime.



That's surprising that water concentrations would be close to dosing levels, unless the concentrations were measured immediately after dosing. Or is the point of EI that plant uptake is a tiny fraction of what is dosed?

Wow, 50ppm! Good thing you have a RO/DI unit.



I'm an engineer, so I'm familiar with conservation laws but as you state the point of the water conditioner is to react with harmful compounds to neutralize them, not to somehow remove them from the water (though, it would certainly be possible to cause them to precipitate, which would be removing them from the water column). I would guess a similar reaction mechanism would be how Seachem Prime would "remove" copper and other heavy metals from the water - react with them to form a less harmful compound. Have you ever tested water for copper before and after adding Prime to see what happened? Might be interesting.


That's an interesting point on its effects on fertilizer - my only guess would be that the reacting compounds in Prime are short-lived? Perhaps they preferentially react with heavy metals, but other ions present in water also react with them but at a lower rate. Just a guess; no clue if that's anywhere close to true.
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post #14 of 14 (permalink) Old 01-24-2020, 06:16 AM
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Have you ever tested water for copper before and after adding Prime to see what happened? Might be interesting.
I use RO DI water. there is no need for a water conditioner so I don't use it.

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That's surprising that water concentrations would be close to dosing levels, unless the concentrations were measured immediately after dosing. Or is the point of EI that plant uptake is a tiny fraction of what is dosed?
The samples I collected were just before a water change. Some showed a drop while others you it wasn't clear. Overall I think there are two reasons when I am not seeing a more significant drop from my targets.

When I developed this recipe I Based it on the relative concentration level of nutrient in plants. that world out to Fe 1, Mn0.5, B and Zn 0.2 each and Cu 0.1 And then I set the Fe dose at 0.1ppm wich is a common dose I have seen . Then I adjusted the other nutrient level Mn, (B, Zn, Cu, Mo, Ni) so the relative lives stayed the same. The 0.1 Fe dose may be higher than I need in my medium light tank.

Also I do a 50% water change once a week. So during my water change I only remove 50% of the nutrients. The rest carry over to the second week. So just due to the water and the fresh dose of micros, the levels right after, nutrient levels probably start out higher than my targets. And then those levels drop down tho the values I saw when he lab test was done.

Note I am using this test company for the lab test:https://www.amazon.com/ICP-Analysis-...2-4ca5ff43ebe6

Quote:
Wow, 50ppm! Good thing you have a RO/DI unit.
But is that a toxic level? While this study is not a complete answer to the question it does suggest 50ppm might not be toxic:https://www.researchgate.net/publica...h_water_prawns
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