Phosphate starvation and nitrate uptake - The Planted Tank Forum
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post #1 of 16 (permalink) Old 06-16-2006, 03:49 PM Thread Starter
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Phosphate starvation and nitrate uptake

A very small and pretty unscientific experiment, but the outcome pleases me. In case this is useful to anyone else.

Just the basics on my tank: 55 gal, about 2.5 wpg compact flourescent lights, flourite/gravel substrate, excel dosing, and dry fert dosing. For filtration I have an eheim classic, an aquaclear HOB, and a submersed powerhead providing extra circulation (with a prefilter attachment). My PH is between 7.0 and 7.2, and do small water changes each week (5-10 gallons). I use ferts in proportion to the EI method, but greatly reduced in amout. I'm generally on top of water testing/changes, but the last two weeks have been hectic in getting my 4 year old adjusted from pre school to day camp.

3 days ago I took a break to do some maintainance and replanting, and tested my water parameters. I like to keep my phosphate low (around 1ppm-- I know, the reccommendation is for 2 or 3 times greater than that, but I'm not going for maximum growth and an amano-style tank), but it had dropped to .25 (and barely that). At the same time, my nitrates had shot way up (at least to 60ppm, and maybe higher than 80ppm). My first thought is that one or both tests had gone bad, so I calibrated them with a test solution but they were both right based on that. I don't really overfeed and I have a well-stocked tank, but I tend to feed high quality food and enough of it so that my large collection of corydoras get enough on the bottom.

Now my experiment/solution: I recalled a Tom Barr newsletter from some time ago (January 2006, as it turns out) on the role of phosphate. That article has more on what phosphate can and can't do than most of us will ever be able to really understand-- but one of the points he documented well was the role of phosphate in the plants' ability to use nitrogen/nitrates. So I hypothesized that the high nitrates in my tank were at least partly due to possible phosphate starvation. The other possible causes were a dirty filter and 2 missed water changes. First I cleaned the eheim, which also gave me an opportunity to remove some of the biological filter beads, as I'm working towards a semi-Walstad approach that allows the plants to take up more ammonia. I changed 5 gallons of the water, my usual practice.

The nitrates were still registering just as high the next day, so I cautiously added 1/16 of phosphate (dry KH2PO4), which should raise levels to approximately 1.5. A check on this later in day suggested this is exactly what happened. Nitrates were down slightly (to definitely 60ppm).

The next day, nitrates were down to 40ppm and the phosphate was down to 1ppm, suggesting both that the enhanced phosphate level had allowed the existing plants to take up some of the excess nitrates and that they were using the phosphate as well. I again added KH2PO4, but I added 1/8 of a teaspoon, on the theory that that plants were obviously using it and even if they used no more (which seemed unlikely), it would bring levels to a 3.3ppm max. I also added my "outside" hornwort to the tank (I have some plant cuttings growing in a black oval bucket outside).

This morning when I tested the tank, the nitrates were 10-20ppm (where I prefer to keep them) and the phosphate level was 2.5. I have noticed remarkable growth in the past 2 days, especially the kleiner bar sword (which has grown slowly since I got it several months ago) and the bronze wendti crypts.

I have been chicken to add phosphate, but this problem and so-far-so-good solution has helped me understand just how useful it is. I really appreciate the information that Tom Barr and others on this forum have provided that allowed me to learn something, and I apologize if I misapplied or misunderstood anybody's method.

Karla
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post #2 of 16 (permalink) Old 06-16-2006, 05:51 PM
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I notice the same thing in my 45. I like to keep NO3 at 20-25ppm and PO4 at 3. If I skip a dose of KNO3 and KH2PO4, my PO4 level goes low, but my NO3 goes UP. Now it is obviously not increasing due to overdosing, because I MISSED a dose. I also run the risk of GSA.

I have very high light (over 4 wpg), so I have to dose full EI. I've tried other methods, but they don't work for me.

My observations are consistent with yours, and everything I've read from Tom.

Sergio C.
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post #3 of 16 (permalink) Old 06-16-2006, 06:48 PM
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I'm not trying to criticize, but the whole basis of the EI fertilizing method is to add more fertilizers of every kind than the plants need, then use a big water change once a week or so to get rid of any excesses this leads to. So, dosing much lower than EI amounts, with a 2.5 watt per gallon light intensity, loses most of the benefits of EI, and doing only very small weekly water changes loses the rest of the benefits. We need to, as an act of faith, accept that high levels of NO3 and PO4 in the water, as well as high levels of the other ferts, will not do any harm to the plants, and is very unlikely to harm fish. Once we accept that, there is no good reason not to use the full EI dosing schedule and water change schedule.

I didn't see anything about CO2 in your first post. If you aren't using pressurized CO2 yet, that is the single most beneficial addition you can make to the tank right now. Without adequate CO2 the plants can't use the ferts and light you have.

As far as ammonia goes, the plants will use whatever ammonia you have if they are growing well. If you test for ammonia you are very unlikely to ever see any. But, the very brief time any ammonia is in the tank acts as a starters green flag to algae spores - to them, this means it's time to wake up and grow, baby!!

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post #4 of 16 (permalink) Old 06-16-2006, 09:08 PM Thread Starter
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Quote:
Originally Posted by Hoppy
Once we accept that, there is no good reason not to use the full EI dosing schedule and water change schedule.
Sure there are good reasons not to use EI dosing-- if you're not interested in achieving maximum growth, in particular. I pretty much believe that the EI method is best if what you want to achieve the best and fastest plant growth. But having an award-winning tank like you or anyone else is not my goal-- I admire the many beautiful tanks on this forum, but I don't want to do too much trimming and I don't want a co2 tank in my house. I'm not into the technology aspect of planted tanks, and I'm not interested in just doing what everyone else is doing-- even if it is the "best" thing to do in the abstract. I'm not arguing that my method is best or that EI isn't the best.

Actually, I'm not arguing at all. I just don't want to be told that I "have" to do pressurized co2 or follow any particular method. I have to fit my planted tank into the rest of my busy work and family life, and I really like how things are going now. My tank is very pretty-- it won't win any awards nor would it probably be admired on this forum. But I love watching it and so does everyone else, including my hubby and 4 year old. I get many compliments from guests who are probably unaware that my stargrass could be a little thicker and brighter and bushier than it currently is. For them and for me, the pleasure is what's there, not what it could possibly be, if only ____.

But I have learned from reading about the EI method, which was the whole point of this post, and find a particular pleasure in finding my own path to adapt it to my needs.

Karla
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post #5 of 16 (permalink) Old 06-16-2006, 10:49 PM
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None of us has to use any method discussed here, and most of us have learned that you can have a very nice tank using many different methods. We all pick and chose the methods or combinations of methods that fits what we want in an aquarium. For example, I never put much thought into aquascaping - I just want to be able to see the interesting plants, so new ones go where I can see them. The day I win an award for my tank will be the day everyone else has moved to a salt water tank!

So.....I suggest that the best way to achieve what you are trying to achieve is to lower the light a bit. My understanding is that we should always have the light be the thing that limits plant growth, not the nutrients. And, I think that is to give us the best shot at avoiding algae. But, as many others say here, if what you are doing is working, don't change it.

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post #6 of 16 (permalink) Old 06-16-2006, 11:24 PM
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Hi Karla, thanks for sharing this. I have noticed and mentioned that same relation between N and P, when one goes down, the other isn't being used as usual and stays high.

I don't follow EI, my goal is to find the minimum level of nutrients that is necessary to support healthy plant growth. This keeps my fishies in a healthy environment, even if I skip a waterchange for a week or two.

Of course, this works better in a medium light environment where plants don't eat through nutrients as quickly.

I keep phosphates at around 0.5 and nitrates around 10 ppm. Lower than most...


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post #7 of 16 (permalink) Old 06-17-2006, 01:14 AM Thread Starter
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Quote:
Originally Posted by Hoppy
So.....I suggest that the best way to achieve what you are trying to achieve is to lower the light a bit. My understanding is that we should always have the light be the thing that limits plant growth, not the nutrients. And, I think that is to give us the best shot at avoiding algae. But, as many others say here, if what you are doing is working, don't change it.
I don't really follow your logic here. If I were to cut back on the light, then the plants would have less of a need for nutrients. Excess nutrients in the water would require more water changes, or bigger ones, and that is not what I want. Actually, I am achieving what I want right now, although what I learned from this experience is that I need to add more of one nutrient (phosphate) to prevent a build up of an excess of another nutrient (nitrates). It's a bit paradoxical because I, like Wasserpest, want to dose the minimum amount of nutrients for healthy plant growth.

Wasserpest, you hit it exactly right and helped me crystalize my thinking by your "minimum nutrients necessary" approach. It kind of reminds me of something I learned way back when in graduate school, which was that some tasks only needed "minimum effort" to pass, leaving me free to focus my attention on other tasks where my "maximum effort" would be productive and enjoyable.

Your tanks are all beautiful, by the way. I would love to explore your journals at a later point.

Thanks for everyone's feedback. I appreciate it.

Karla
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post #8 of 16 (permalink) Old 06-17-2006, 05:30 PM
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Now folks, EI is simply a general thing, a starting point, it's not written in stone, nor are the suggestions I make about it.

Don't fall into that trap and limit yourself.

EI can be easily changed without a test kit also, you simply slowly reduce the nutrient of interest, in this case PO4.

It's not hard, nor is there any need for a test kit.
You will run into to trouble the lower the ppm 's you go with any test kit.
Accepting that assumption will help a great deal.

Next, simply maintain the higher levels and lower the nutrient down till you get a negative plant or algae response.

You need to maintain good non limiting conditions for the other nutrients when you do this and it takes about 2-3 weeks to get a good feel for how the limitation works.

It does not have to be PO4 either, CO2 works better if you ask me and achieves the gaols of less work... better than PO4 limiting.

But the trade offs each limitation provides is what you will want to focus on.

If you run the PO4 down low, the NO3 does not need to be as high.........but.........if it is high, it's not an issue if you do the water changes either.

But KNO3 is roughly 22$ for 50lbs, I really could not give a hoot if I wasted 2x as much at those cost for my 50 gal tank.

But either way is fine(high or low NO3 if you limit say CO2/PO4).

Simply reducing the amounts dosed progressively and slowly till you hit a negative response is all one needs to do if they prefer to try a lean version.

Amano's tanks are not quite as lean as he may lead you to believe either.........I know folks write things about their parameters and they fudge them.

They also .......as everyone here knows............change day to day and hour to hour depending on the nutrient in question, Amano is not providing standard error and variation over a week, over any time frame.

Water column nutrients also will tell little if you have a fair amount of nutrients in the substrate, if you run things leaner in the water column.

If you seek to slow down growth, stop adding so much light.

"I want slow growth and healthy fast growing stem plants but I want 5 w/gal"

Use things/methods that do not oppose and are not anatagonistic towards one another.

Use less light first, then CO2, then PO4.

A smart aquarist will simply add a nice scape with wood/rocks etc to replace all the faster growing stem plants or switch from fast growers to more electic slower growers and Crypts etc so they prune less.

Why keep weeds and expect them to grow slow?



I'm not sure why folks paint themselves into a corner and assume such rigid approaches, EI is a very flexible methiod and allows anyone to modify and change things simply by reducing or increasing the volumes of ferts dosed.

This is much easier than testing and assuming the test kits are correct/calibrated correctly, the volume of KNO3 per unit tank volume over time is a much simpler thing to suggest and to standardize for folks when giving advice.

The question is what is gained by lowering the nutrients, the answer is slowing the plant growth without getting algae.

Non CO2 tanks beat any method for that one.

Now you still want to add CO2, well....best option is to reduce the fast weedy species.

There are many goals and constraints we place on a method.
Being able to achieve the goals you want with a method is another matter, 99% of the issue is you, not the method itself.

If you can do each method successfully, then you can better judge and use such methods to achieve various goals you may have.

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post #9 of 16 (permalink) Old 06-19-2006, 01:30 PM
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Thanks for bringing this up. Not to steal a thread but had some similar thought and experience this weekend.

After doing some reading here and looking at what was happening in my 55 I had a plan of attack.

Substrate had become anaerobic and needed a stir. ID this with the crypts starting to melt and general oily surface scum for the last few weeks.

I had let my usual dosing go on for so long that the plants seemed to be starving. Come to find out I was at the very bottom of the normal accepted % of KNO3 and PO4. Probably had been for a few weeks, I hadn't tested in a while.

This weekend was the time to correct the ferts and get the substrate back in order. So after stirring the substrate in some dead corners and around the crypts I performed a 40% WC. Then cleaned the pump lines, I needed to install a new UV bulb so good timing. After placing the correct amount of ferts to bring the KNO3 to 10 and the PO4 to 1 I wait till the afternoon to do some comparative tests.

KNO3 was at 20+ and PO4 never changed much????

As of this morning and still adding/monitoring the PO4 is down to .5 again and the KNO3 is back to 10.

So I wonder if stirring the substrate caused the Nitrate spike and has now setteled? Or are my plants really taking on this much each day? Is the PO4 being used that much???

I'm going to resist kicking up mulm but if it gives me a kick of Nitrate that is being absorbed I won't stress too much and get this substrate back in order.

Keep in mind this is a mature tank about 2.5 years old with around 2wpg.

I'm placing around 20+ drops of fleet every other day and 100 ml of KNO3, K, and Mg. The latter using a mixture with the following 700ml RO water, 1 TBS Potassium Phosphate, 1TBS Potassium Nitrate, and a little Epsom salts.

So do I up these macros a bit more to keep the levels up? All indications say yes according to tests and what the plants are doing...

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post #10 of 16 (permalink) Old 06-19-2006, 03:55 PM
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We had seen the slowed uptake of NO3 via low/limiting PO4 levels for many years........

This is nothing new here.........it's just been brought up again.
Folks that did the PMDD method outlined by Paul Sears obviously experienced this issue of slowed NO3 uptake and slower growth since all those tanks pushed towards PO4 limited tanks.

While many like to think Amano's tanks are all that way, you may want to rethink that. You can look and tell what a health non limited plant looks like and that is a better gauge than a cheap test kit or a one time measurement that does not take inot account the substrate nutrients nor the water column nutrients over a week's time or longer.

Plants can store a lot of nutrients, so the test need to be long enough to depelete such reserves, additionally, accounting for substrate sources of nutrients is also critical obviously.

A plant can withstand PO4 limitation better than NO3 limitation as a rule.
But if you want less growth, be wise about this, use less light, the plants will grow fine, just slower.

That will make the NO3/PO4/CO2 dosing much easier and allow more flexibility and provide a much better method to slow the growth rates while maintaining healthy plants as well as reduce the potential for algae considerly.

PO4 limiting does not limit algae..........in encourages green spot among others. PO4 limiting also slows NO3 uptake, but as such, it also slows NH4 uptake also, which is not good.............

The substrate vs water column idea is based on one thing, avoiding algae, we know that limiting the water column does no good there, many have claimed that but clearly the observations are counter to that and this observation is very old and wide spread.


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post #11 of 16 (permalink) Old 06-19-2006, 05:30 PM
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So what your saying Tom is keep the PO4 up to keep the NO3 and NH4 available. Didn't think of this relationship till this thread. Thanks for the info.

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post #12 of 16 (permalink) Old 06-19-2006, 10:26 PM
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Hi,

I'm saying if you want to manage the plant growth, reduce the amount of growth and still provide nice health and coloration with low/less algae issues, it's better to use less light and maintain good nutrient/CO2 levels.

This is much easier, cheaper and will give you better results than limiting PO4.
The uptake of NH4 will still be quite high even at moderate to low light.

Plants really hate K+ and Nitrogen limitation, PO4 can be more flexible, but.......since it's not a large lake or some large scale environmental concern, simply add less light, that's cheaper for everyone over time and yeilds better results.

I've already done all this monkeying with nutrients, you are welcomed to play around with it, but over time you will find similar patterns/results/conclusions.

Most folks today do not recall all the PO4 limiting tanks of the 1980's-1990's, everyone did it when it was en vogue. Most folks here don't have more than few years in the hobby/on the web etc.

Adding PO4 dramatically increases everyone's growth and got rid of stalled tank snydrome.

The other benefit besides less NH4 is more O2.
Limiting a plant at high light with PO4 reduces the O2 produced by plants.

At low light, the O2 is maxmized for that given light intensity.
The only limiting factor is light at that point.

Light is the main input of energy, it drives everything else in the tank, therefore it is the best and most logical place to "limit" growth in a manageble way.

This way, you can dose liberally the nutrients without worry/issue, and dose the CO2 etc with greater flexibility.

Lower light is easy to control once set, maintaining a knife's edge level of PO4, NO3, Fe etc is much harder and requires far more testing, maintanece and attention.

Regards,
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post #13 of 16 (permalink) Old 06-20-2006, 07:47 AM
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It does not have to be PO4 either, CO2 works better if you ask me and achieves the gaols of less work... better than PO4 limiting.
Wowsers. This was a new one for me personally. I have the impression that if I make the smallest mistake with my CO2-levels things will go sour very fast. If I limit CO2 I also get very small new growth on most species.

Or did you mean some kind of low-tech approach without artificial CO2 but with CO2 from bacteria/fishes/substrate?


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post #14 of 16 (permalink) Old 06-20-2006, 03:57 PM
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No, not at all, the issue is still light, you do not use the same light intensity on a non CO2/non Excel tank as you might with CO2.

Adding CO2 to a low light tank will dramatically increase growth also..........but everyone always thinks of CO2 associated with high light tanks...........

So the rate of growth is really the issue and what increases and decreases that.

There are two basic regions, actually more but they tend to tougher to hit, that CO2 is useful or lack of it is also useful.

One of the main thibngs is low variation with the ppm's of CO2.

So if you add CO2, add 30ppm or so and keep it there.
If you do not add CO2, then do not do water changes which add CO2 back and remove the nutrients/cycling that provide the plants, little spikes in the CO2 can hurt plants and confuses them when the CO2 is all over.

Algae take advantage of that variation and rightly so.
Algae prefer CO2 as well.

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post #15 of 16 (permalink) Old 06-20-2006, 05:29 PM
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So if you add CO2, add 30ppm or so and keep it there.
If you do not add CO2, then do not do water changes which add CO2 back and remove the nutrients/cycling that provide the plants, little spikes in the CO2 can hurt plants and confuses them when the CO2 is all over.

Algae take advantage of that variation and rightly so.
Ahh ok.. That was what I was hunting for. Though I had missed something. =)


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