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Discussion Starter · #1 · (Edited)
This is a dosing related thread that is focused strictly upon plant uptake of fertilizers that we add (although, drifting off-topic is fine). As most realize, we don’t have a good handle on this, but it is an important part of trying to maintain targeted levels of nutrients. It is not so important to the EI user, since that concept simply slops on more-than-enough fertilizer and resets with large and frequent water changes and the wide swings in fertilizer levels between water changes are ignored. Many of us prefer a more tightly controlled approach, and the tighter we try to control it, the more important the need to identify plant uptake becomes so that we don’t bottom-out at any point.

Several of us have been discussing what has always been something of a futile effort to measure plant uptake of nutrients. To our knowledge, we have not seen a consensus on a good method for doing this. There are plenty of random comments about it scattered throughout this forum and the Internet generally. We were hoping to use this thread to try to gather opinions and methods used by members to measure/determine uptake and this can include simply stating what uptake numbers you might use based upon studies that you have found elsewhere (please provide sources, if possible). To this end, I open this thread to any member willing to express themselves on the subject.

There are many, many variables that impact uptake. The primary variables that come to mind are plant mass and type of plants, nutrient interactions (a la Mulder’s charts), pH levels, light, CO2 and [you add some]. Since each tank has it’s own mix of these, stating an uptake number may not be as useful as providing the method for determining it. With a method identified, any of us can then run to our own tanks to try it. However, citing a number, while less useful, might also be revealing if we find a reasonable range that seems to be consistent among tanks. This is where citing sources might be useful, e.g.; I’ve found many useful studies that originate in the aquaponics and hydroponics area.

My input:

The basic way that I determine uptake is to simply use the before and after approach: take readings after a water change, take another reading just before the next water change, add what was dosed and the result is the uptake. Of course, the quality of test methods and tools will increase or decrease accuracy. I’ve found this to be a reliable method for K, Ca, Mg and Fe, as well as the parameters pH, dGH and dKH. However, the other elements become less firm, beyond this.

NO3 and PO4 are a little more difficult for gauging uptake, because we have animals and other things adding to it that we can’t measure well. So, measuring these two elements one day, then measuring them x-number of days later, doesn’t give us a great idea about uptake. Further, in the case of NO3, it would be good to know how much Nitrogen (N) is actually used and, in this case, it involves all of the N sources (NH3-N, NH3-N, and NO3-N). We usually, without thinking about it, use NO3 as a proxy for all N. One link that I’ve found that might provide some use in this area is here: N uptake(?).

Hobby-grade tests for measuring traces (other than iron) don’t exist, so this leaves us mostly blind and, like all of the elements, heavily reliant upon trial and error by observing plants. Currently, I am working with a lab that has just introduced the ability to measure in ppb (a mass spec test). I will report on my findings over the next month or two on that.
 

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Your state's agricultural extension can be an invaluable resource for more specific and detailed testing at a fairly reasonable price. For example, Georgia's Ag Ext. can test for the stuff on this website: AESL Fee Schedule

They can usually do plant tissue nutrient and substrate/soil analyses as well.

When trying to quantify uptake in your tank here are a few things to consider:

1. NH3/NH4 are typically converted to NO3 almost instantly by the filter so we don't need to worry too much about measuring that. The main confounding factor is how much NH3/NH4 our plants are taking up. For our purposes and abilities to test a standard NO3 for water quality and Total N on plant mass should be sufficient.

2. When testing for how much you're actually adding per-dose, test right before your water change, add the nutrients AFTER filling the tank and turning the filter on, wait about 10-15 minutes to let things mix then take your water sample. Speaking of water samples, it's good practice to take a good amount of water (2 cups should be sufficient) out of the tank and keep it in a glass container. Fully rinse the container in the tank water at least three times to make sure any residual materials are washed off.

3. Since uptake rates are influenced by total plant mass, put a measuring stick in the tank every couple days and note the height (length) of each plant. If it's something that grows from a central point (Crypts, Swords, etc), measure the longest/tallest leaf.

4. Standard practice for starting a new aquatic plant study is to let the plants grow for a couple weeks to make sure they've adapted to the current environment. After that, remove them, measure total length, cut the top 15 cm of the stem to replant. For things that grow from a central point, removing all but the newest 3 leaves is normal. In this case, getting a basal stem count is useful; it'll tell us how many new leaves the plant grows over time. It can be done with stems as well since many of them throw off branches.

I know this sounds harsh and a bit scary, but having a standard method like this will help us compare relative growth rates and has the added benefit of (probably) providing enough plant mass to have an initial tissue nutrient analysis done.

5. Preparing plant tissue for analysis-

If you want to get super fancy-pants and think you have enough of various single species to get at least 2 grams of DRY biomass and want to foot the bill to have tests run on different species, that would be cool. An aggregate test of all species in the tank should be sufficient to get an average uptake amount. Chlorophyll content is usually an option as well if you want to get super-duper fancy pants.

*Get some medium mesh bags, laundry bags for delicates work well for this.

*Cut your plants and rinse them gently under lukewarm tap water to remove as much epiphytic algae as possible. Don't remove leaves with GDA; the biomass from that is insignificant.

*Don't worry about removing roots; even when testing Vallisneria in my study, the root mass was not a statistically significant portion of total biomass.

*Take your cuttings and press them between cloth towels to remove as much water as possible. A gentle patting is enough, you don't want to break leaves off.

*Put a modest amount of cuttings in the bags, making sure to not pack them so full that air won't get in, then hang them to air dry for at least 24, but no more than 48 hours. A cheap laundry rack and fan work very well. It's best not to hang them outside if at all possible as humidity can cause them to not dry fast enough and/or cause mold to form. If you've got a lot of long stems or big leaves from Crypts etc, go ahead and cut them into 4-6 inch portions before bagging.

*Carefully put the dried material in a PAPER bag, leaving the top open, and store in a cabinet (closed, dark, cool, dry area) until you're ready to send the samples off.

*Contact the testing facility to see how they want the cuttings to be sent out and await your results!

6. Water testing: contact the testing facility to see how they want samples taken and shipped. Some tests require pre-treatment with acids, which the facility normally provides in a sampling kit that's sent to you.

That should be enough for now. I'll see about working up a standard method and spreadsheet for tracking nutrient input and relative consumption later.
 

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Discussion Starter · #3 ·
I'll look forward to the spreadsheet, if you get the time.
 

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Discussion Starter · #5 ·
I have no idea. I know that @Greggz has done it. Maybe he can help.
 

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This is Gold, thanks!

Do you think it would be used to test Aquasoils (like ADA) if they're under a year old?

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I'm pretty sure your local Ag Extension or state's Land Grant University, for me that's Univ. of Georgia, has a lab that can analyze any soil sample you want to send them. If it's something like Flourite, Black Diamond Blasting Sand, or Eco Complete, make sure to confirm they can do metals analysis on rock first. If not, there are labs out there that can.

Sadly, it turns out I can't attach an active spreadsheet to a message here. If you guys feel comfortable messaging me an email address I'll be happy to send it out to you. We can then share screenshots as time goes by.
 

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Discussion Starter · #11 · (Edited)
@Wasserpest:

Is it possible to do this, or to upload a spreadsheet to our profiles:


Sadly, it turns out I can't attach an active spreadsheet to a message here. If you guys feel comfortable messaging me an email address I'll be happy to send it out to you. We can then share screenshots as time goes by.
@somewhatshocked:

Wasserpest name doesn't seem to indicate a link. Is this the way to contact the admin?
 

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The @ naming method will send a notification to that user, provided they have turned on notifications :)
@Wasserpest seems to work for me though!

For a spreadsheet, I do not think it is possible (I haven't tried personally). I would imagine a Google Spreadsheet would work though? You can easily adjust permissions to only allow certain users to edit the spreadsheet if need be.
 

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Discussion Starter · #13 ·
For a spreadsheet, I do not think it is possible (I haven't tried personally). I would imagine a Google Spreadsheet would work though? You can easily adjust permissions to only allow certain users to edit the spreadsheet if need be.
Thanks, Anthony. The Google idea seems to work.

Phil Edwards:

Try this link to see if you can manipulate the data in it: Nutrient Accumulation

You have to have a Google account to manipulate the data but, if you don't, we can still see the frozen spreadsheet.

If it works, then you have a way to share your spreadsheet (if you have a Google account). You can, simply, upload an Excel spreadsheet into this Google spreadsheet, then post the link.
 

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I’ve been waiting to chime in on this discussion, as I kind of wanted to see where it was going first. My first thought is that we will never precisely quantify uptake of nutrients. However, I do believe that having a ball park estimate can help one better understand what is happening in their tank.

I’ve messed around with this for years. In my tank heavily planted and full of Rainbowfish, I estimate my nutrient uptake and tank generated nutrients to be very close, with the tank generating just a bit more than fish provide. But even this can change based on how much plant mass is in the tank. After a good trim my TDS rises slightly during the week. But if I let the mass get out of hand, the TDS actually decreases during the week.

How do I come to this conclusion? Years of testing and applying what I think to be reasonable estimates based on my experience and what I have read elsewhere. Pretty scientific, huh? I’ll be the first to admit I might be completely wrong. That’s why I am very interested to hear what conclusions others have come to.

Now the next question would be if we can quantify the uptake, how would we use that information? Some might think if I know my plants are using up 2 ppm NO3 per day, then I need to dose 2 ppm NO3 per day. Personally, I don’t think so. I am a believer that there is an optimal amount of nutrients in the water column that makes it easier for plants to uptake those nutrients. I also believe that if that is true, then it would make sense to try and keep the levels at that optimum number.

When you start going down this path, you also need to take into account dosing amounts, dosing intervals, water change percentage, and accumulation. Combine that with tank generated nutrients (fish/other waste) and plant uptake and you can get a better understanding of why your water column numbers are what they are.

The first thing one needs to understand is how accumulation works. Here is an example showing typical EI dosing every other day and assuming no plants or fish. This is the theoretical maximum accumulation of nutrients. It’s theoretical because it does not take into account any other factors. After about 10 weeks the tank hits it’s max accumulation. Then with traditional EI, one performs a 50% water change which removes 50% of the nutrients. Pay attention to the Daily NO3 level in week 11. As more nutrients are dosed the nutrient level rises slow throughout the week. In my opinion, this is one of the weak spots of EI dosing. The water column level has a wide swing throughout the week.

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To illustrate how much water change affects accumulation, let’s change the water change percentage to 70%.

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This illustrates that if you are copying someone’s dosing (or following a manufacturers recommended dosage), your water change percentage means a great deal. Two tanks dosing the same amount of nutrients but with different water change percentages have much different theoretical accumulations.

Let’s go the other way. What if one is only changing 30% water weekly? Then accumulation is much, much higher.

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Now let’s go back to the first example with 50% water change. Let’s estimate the plants are taking up 2 ppm of NO3 per day. Here is how that looks. Again, pay attention to the daily levels.

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Note that the NO3 accumulation goes from about 42 ppm to about 14 ppm at the end of the week.

Now we add a modest fish load and estimate tank generated NO3 at 1 ppm per day.

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Peak NO3 goes from about 14 ppm to about 28 ppm. Now we start to understand how much plant uptake, tank generated nutrients, and water change percentage affects the amount of nutrients in the water column. This is one of the reasons why blindly following someone else’s dosing can produce quite different results. The actual water column levels of nutrients can be quite different.

Here is what I “think” is happening in my tank. I dose 16 ppm NO3 and perform a 70% water change. I also “front load” all macros, so that is a single dose for the week right after a water change.

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Once again note the Daily NO3 level. It stays very steady somewhere right around 25 ppm. I can tell you that if I test my water any day of the week it looks to be right about 25 ppm. I can also test my TDS and it stays very steady. In fact, my TDS after a water change is almost the same as right before.

Now does that mean these numbers are accurate? No. Pretty much an educated guess. Would knowing the precise level of uptake make a difference? Not really that much, and in reality it changes pretty much every day based on plant mass. But I do believe having a good ball park idea can help one understand their tank and is a great help in developing a dosing strategy that makes the best sense for their tank.

And all that being said I am still very interested in hearing others thoughts. Both how they estimate plant uptake, and then how they would apply that knowledge.

If anyone wants to mess around with my spreadsheet, I have it uploaded to a Google Drive. You can download it here and use it any way you like. Keep in mind the cells out outlined in red are the only numbers you need to enter. Everything else is calculated from those entries.

GreggZ Shared Files
 

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I want to do this simply out of personal curiosity and it would be cool to have some sort of (semi-scientific) record from the Hive Mind. This is also one of the reasons I'm sending the tissue samples to the lab for analysis. I'd like to know what the total dose between samples is, what the (general) uptake and accumulation rates are between water changes, then compare that to the total nutrient content the plants have incorporated over time.

It's all monkey braining being a nerd type stuff, but who knows, it may end up being useful at some point.


I don't have time to read through your full manifesto at the moment. I'll digest it over coffee in the morning. :)

Hey all,

It looks like there was an issue with access. Try this instead, it should be open to the public.


Thanks!
 

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Discussion Starter · #16 ·
Update regarding the testing of water parameters:

1) Testing the Testers

I had intended to get at some better consumption estimates by comparing accumulated estimates of nutrients dosed, to water test results as performed by commercial labs. Unfortunately, these labs have left me with the belief that their capabilities are highly unreliable. I used two types of labs; commercial and university. For the commercial labs, I considered three commonly mentioned labs in the saltwater world and, which, have also been frequently mentioned on this forum. One of them simply stated that they do saltwater only, which left two that will do freshwater. I don’t want to mention names, but will do so via PM, if anyone is interested.

I’m not looking for precision or a perfect match in the test results. Lab tests that aren’t very expensive are only going to be close and our calibration solutions are only going to be close, even though we may start with large stock solutions for dilution. The utility will be if I can see a reliable ballpark reading from my tank water tests but, first, I needed to know if the commercial lab results could be trusted. The conclusion: they cannot be trusted.

To calibrate these lab tests, I created a calibration solution combining NO3, PO4, K, Ca, Mg, S, Cl, Mn, B, Cu, Mo and Zn. Utilizing various salts, nutrient calculators, and large initial stock solutions, I was able to affirm that the stock solution was accurate for the macros, using our hobby grade test kits. For micros, I am entirely reliant upon a testing lab to confirm my stock solution accuracy.

Both of the commercial labs that offer freshwater tests were so far off of the calibration solution values as to be laughable. The variances in the results from these labs were double, up to quadruple, actual values, and these worsened as ppm values lessened, such as with traces. Compounding this was the fact that I sent 2 or 3 samples to each lab, weeks apart, from the same container of calibration solution and, at a minimum, I would expect that the test results would be similar to each other, but even these results were all over the place, i.e.; they tested the same water 2-3 times and reported dramatically different results each time.

However, the university results were very close to the calculated levels in the calibration solution. Without hesitation, I will now use this university for my tank analysis. I chose Penn State for the university test. Penn State has a large agricultural curriculum and, in support of this, they offer tests designed for, as they put it: “Irrigation Water for Nurseries and Greenhouses.” All of the key elements we are interested in are included in the test. I suspect that any university with a large ag focus would do the same.

2) Testing the Tank Water (utilizing PSU)

As with the calibration solution tests, the macro results came in close to my hobby-grade test kit results. However, the traces were a surprise. First, I don’t consider iron in the results. I use only Fe gluc and it’s brief life span in tank water is better gauged with my Nutrafin kit. In my case, I use Mn as the proxy and build ratios of B, Zn, Cu and Mo off of the Mn. similarly, my trace stock solutions don’t contain the Fe gluc.

I’ve been playing around with traces, recently, and had created a mix that I was testing for several months. My plants have been growing well, but not as well as they had been, particularly my Pantanal, which has developed very poor new growth (I’m actually trying to resuscitate it, at the moment). I use my own nutrient accumulation spreadsheets and had started with the assumption that the uptake rate for my trace dosing was 25% and I keep theoretical accumulation spreads (peak to valley) of +/- 12.5%. well, the PSU test on my tank water indicated that I had fallen well below desirable levels, possibly to zero as they were below .01ppm (<.001 for Mo) …except Boron, which tested at what I consider the toxic level of .15ppm. Remember: PSU tested accurately for traces in my calibration solution.

3) Early Presumptions

A month or so after introducing this new trace dosing, I’ve noticed some chlorosis in my Dwarf Sag (Fe and N is plentiful), crippled new growth on several plants (Pantanal previously mentioned) and extreme brittleness in my Aromatica (top several inches). These are all potential boron toxicity issues. Speculating, based upon the PSU results; I’m probably just barely giving enough metals to live and boron is not being consumed like the other metals. The excess boron seems to support a boron toxicity rather than deficiencies of other nutrients, particularly since my moderate levels of N, P and Ca shouldn’t be limiting boron uptake. It’s a mystery to me.

In any case, based upon the PSU test results, I’ve revised my trace dosing, including dramatically lowering boron, and will see how things go these next few months. The other traces are increased as a function of my nutrient accumulation calculations, which now assume a 35% uptake (from the previous 25%) of the chosen dosing levels. My objective is to see if I can establish trace levels that conform to the accumulation patterns and, therefore, find the uptake % for each.
 

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Hi @Deanna

Very interesting thread.

Recently, I've been measuring PO4 uptake in one of my tanks. I add a dose of Seachem Phosphorus and then measure PO4 in the water column. One or two days later, I re-measure PO4 before feeding the fish again. No water changes during this time. I am unable to measure PO4 excreted by the fish. Ideally, I would do this experiment in a fishless tank. So, unless I'm overlooking something, the difference between the two PO4 measurements should be the PO4 taken up by the aquarium plants. Note also that I am using an inert substrate.

I use the JBL PO4 (sensitive) test kit, which will measure as low as 0.05 ppm. The increments are <0.02, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, 1.2 and 1.8 ppm.

Anon
 
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