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Hoagland solution as an alternative to EI dosing

What will happen to any plants added to the tank?

  • They'll melt or exhibit deficiency symptoms.

    Votes: 0 0.0%
  • Results will vary largely by plant.

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    4

AlexVojProc

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What is the Hoagland solution?
The Hoagland solution is a nutrient solution developed in the 1930s-1950s. It was originally developed by Hoagland and Arnon for use in hydroponics, as detailed in their 1950 paper "The water-culture method for growing plants without soil". Since hydroponics is the growing of regular plants in an inert substrate, the thought occurred to me that the Hoagland solution may be appropriate for growing aquatic plants. The solution provides all the nutrients necessary for plant growth, and works well for growing a variety of plant species: in the scientific world, it is widely used to prepare plant cultures.

Isn't this just like EI dosing, but from the 20th century?
Compared to EI dosing, the Hoagland solution is very concentrated for aquatic plants: it includes 610 mg/L in nitrate alone. But, diluted to a 1/10 scale, it doesn't seem too extreme, especially for tanks without livestock. At this concentration, it would contain:
  • Nitrogen (as KNO3 and CaNO3) - 21 mg/L
  • Potassium (as KNO3) - 24 mg/L
  • Calcium (as CaNO3) - 20 mg/L
  • Phosphorus (as KH2PO4) - 3 mg/L
  • Sulphur (as MgSO4) - 6 mg/L
  • Magnesium (as MgSO4) - 5 mg/L
  • Boron (as H3BO3) - 0.5 mg/L
  • Iron (as Fe-EDTA) - 0.5 mg/L
  • Manganese (as MnCl2) - 0.5 mg/L
  • Zinc (as ZnSO4) - 0.05 mg/L
  • Copper (as CuSO4) - 0.02 mg/L
  • Molybdenum (as Na2MoO4) - 0.01 mg/L
Some of these elements -- especially some of the trace metals -- may seem unfamiliar, but I guess they're already included in standard trace nutrient solutions, and they are generally present as impurities in tap water. Since I'm using RO/DI water, and I had them on hand, I've decided to add them anyway. Compared to EI, the Hoagland solution contains 4 times the nitrogen, similar potassium, 3 times the phosphorus, half the magnesium and similar iron.

The experiment
To me, these ratios seem a crazy change from EI, which is very familiar at this point. But, I'm considering trying this out on a new 240L high-tech tank. 30 ppm CO2, high light, all the usual. I might also consider adding pentanedial (glutaraldehyde/generic Flourish Excel). Does anyone have any suggestions, warnings, revisions or predictions before adding plants?

Measurements so far
I've filled the tank and added the above fertilisers. The worst case scenario is that I do a 100% water change, which isn't too painful. Since I don't have access to any proper equipment, I'm going to be using API's test kits. Here are the relevant results in the empty aquarium:
  • My first worry was KH, since the only buffer in here is the potassium dihydrogenphosphate (KH2PO4). I'm aiming for 3 dKH, but getting 1-2.
  • This might be because of my low target pH of 6.5, although I'm getting 6.8. The higher pH may be because I made a mistake and dosed 4 mg/L ammonia, which is basic, as I forgot what I was doing and thought I was cycling the tank. Water changes should even this out eventually.
  • Nitrate is at 50 mg/L.
 
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dw1305

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Hi all,

Hi Alex, welcome to the forum. I'll go through the questions a bit at a time.
The Hoagland solution is a nutrient solution developed in the 1930s-1950s.
Yes, you can use Hoagland solution, it is just an expensive option and time consuming to make. An <"all in one mix"> is a cheaper option, but I used to make my own <"Long Ashton" solution"> for experimental work.

There are a <"a number of nutrient mixes"> that were developed, as hydroponics became more widely used commercially, for Tomato growing etc. They all work, because <"an ion, is an ion, is an ion in solution>", every NO3- ion is the same as every other NO3- ion. Commercial growers manipulate the ratio and concentrations of the elements to promote flowering or leaf production, or for more sensitive crops (Orchids, Azaleas etc.) etc., but for most plants it doesn't make much difference.

It is worth noting that, because ammonia isn't toxic to plants, and plants require a lot of fixed nitrogen, commercial hydroponic mixes tend to contain a lot of ammonia (often from ammonium nitrate (NH4NO3)).
may seem unfamiliar, but I guess they're already included in standard trace nutrient solutions,
They are, <"plants require trace amounts"> of boron (Bo), zinc (Zn), copper (Cu) etc.
Since I don't have access to any proper equipment, I'm going to be using API's test kits.
You won't get accurate enough values with these, conductivity would be a better measure. Have a look at <"Accurate testing ....."> and linked threads.
My first worry was KH, since the only buffer in here is the potassium dihydrogenphosphate (KH2PO4). I'm aiming for 3 dKH, but getting 1-2
OK, this is because KH2PO4 is an acid (you have two hydrogen atoms), and the tests for dKH actually measure alkalinity. You've added an acid ("H+ ion donor"), so alkalinity has declined.

The conjugate base for KH2PO4 is K2HPO4 (which is a base or "H+ ion acceptor", because you have two potassium atoms) and together they are phosphate buffers which you can combine together, in differing proportions, to make <"buffered solutions of a known pH">.

Carbonate hardness (dKH) is also a measure of a buffered system, but in this case the acid and base are CO3-- (HCO3-) and H2CO3 (from CO2). If you want to add carbonate hardness you can use potassium bicarbonate (KHCO3) (or potassium carbonate (K2CO3)), have a look at <"Questions regarding....">, there are amounts to add at <"James' Planted Tank">
Adding 3.6g Potassium bicarbonate (KHCO3) to 100 litres of water will raise the alkalinity by 1
The higher pH may be because I made a mistake and dosed 4 mg/L ammonia, which is basic, as I forgot what I was doing and thought I was cycling the tank.
You don't need to cycle a planted tank with ammonia, it is probably actively harmful, have a look at <"do I need to cycle....">.

cheers Darrel
 

AlexVojProc

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Thanks everyone for the responses.

Yes, you can use Hoagland solution, it is just an expensive option and time consuming to make.
Why would this be better then EI ? Sure you can try this, but i fail tom see the advantages.
I already have the chemicals on hand. I was wondering whether I'd achieve better results with this in comparison to EI dosing, and whether there were any immediate disadvantages in doing so.

I used to make my own <"Long Ashton" solution"> for experimental work.
I've been looking for this article for ages but I'd forgotten the name. Thank you. It's interesting that you used the Long Ashton solution; is there any reason in particular you chose this?

They are, <"plants require trace amounts"> of boron (Bo), zinc (Zn), copper (Cu) etc.
Good to hear. Since I have somewhat large quantities of all of these micronutrients, I chelate the salts myself using sodium edetate (EDTA). Since the pH is below neutral, using EDTA isn't too much of a problem.

OK, this is because KH2PO4 is an acid (you have two hydrogen atoms), and the tests for dKH actually measure alkalinity. You've added an acid ("H+ ion donor"), so alkalinity has declined.

The conjugate base for KH2PO4 is K2HPO4 (which is a base or "H+ ion acceptor", because you have two potassium atoms) and together they are phosphate buffers which you can combine together, in differing proportions, to make <"buffered solutions of a known pH">.

Carbonate hardness (dKH) is also a measure of a buffered system, but in this case the acid and base are CO3-- (HCO3-) and H2CO3 (from CO2). If you want to add carbonate hardness you can use potassium bicarbonate (KHCO3) (or potassium carbonate (K2CO3)), have a look at <"Questions regarding....">, there are amounts to add at <"James' Planted Tank">
I'm aware of the acidity of potassium dihydrogenphosphate and that 'KH' is actually a measure of alkalinity. I have used potassium dihydrogenphosphate/hydrogenphosphate buffer solutions for tissue cultures in the past. The reason I used a KH indicator is because the KH kits are titrations, and I figured that if the end point of the titration is below the phosphate buffer pH, measuring the KH would indicate how well the solution was buffered. After doing more observations, it seems the end point of the API test kit is too high and no amount of phosphate buffering to pH 5.5 will increase the apparent KH. If I wanted to buffer to higher pH, I'd add a (hydrogen)carbonate or (mono)hydrogenphosphate as you mentioned.

At the end of the day, there's probably negligible difference the more I think about it. As long as none of the plants have deficiencies due to underdosing or are inhibited due to overdosing, the plant cells will probably become saturated with mineral ions pretty quickly and nothing will make much difference within reason.
 
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ceg4048

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I already have the chemicals on hand. I was wondering whether I'd achieve better results with this in comparison to EI dosing, and whether there were any immediate disadvantages in doing so.
Hi
No, generally there should be no advantage, however, it can often be the case that the flow/distribution in the tank is poor and using higher amounts than the standard EI recipe may yield an improvement simply because the target concentrations are not actually being "seen" by the plants using the standard dosing.

What's important to know is that dosing more than the standard concentration does no harm, other than the rise in TDS, but neither it it really necessary. That you already have the product on hand is the good news, but it would not be a good idea to go out of one's way to purchase it.

I also think it's a mistake to focus on any target pH. This is always problematic because adding CO2 will always create pH variations. Neither the fish nor the plants will care about the pH, so it is an unnecessary objective.

Cheers,
 

dw1305

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Hi all,
It's interesting that you used the Long Ashton solution; is there any reason in particular you chose this?
Not really, it was just the UK version of Hoagland solution. It was pre-WWW and it was the recipe in the book I was given.

A former colleague had worked at Long Ashton Research Institute (now closed), and we still had links.
Since I have somewhat large quantities of all of these micronutrients, I chelate the salts myself using sodium edetate (EDTA). Since the pH is below neutral, using EDTA isn't too much of a problem.
I used to make it up a separate micro-element solution, you don't actually need EDTA, you can use water and just acidify it to stop precipitation. One batch of micro-element solution would last me years. If you PM me your email address I can send you an excel file with the workings for making up the micro element solutions etc.

You can make an iron EDTA solution (using the sodium EDTA salt and iron sulphate), but you can also buy iron EDTA as the monosodium ferric salt (C10H12FeN2NaO8). Sodium (Na) is the least strongly bound element and Iron (Fe) is the most strongly bound one, so you can make any other chelates from the sodium salt, but once you have FeEDTA you can't bump the iron off (it photo-degrades to release ferric (Fe+++) ions in the tank).
'KH' is actually a measure of alkalinity.
The tests measure alkalinity (titrimetrically), but the dKH is strictly a measure of the (bi)carbonate ions (as HCO3- or CO3-- dependent upon pH).

You can only increase dKH by adding a carbonate, <"either as part of the D/TIC">, or as an insoluble carbonate compound (usually CaCO3). Have a look at <"question on diy 4 dKH....">.
At the end of the day, there's probably negligible difference the more I think about it. As long as none of the plants are have deficiencies due to underdosing or are inhibited due to overdosing, the plant cells will probably become saturated with mineral ions pretty quickly and nothing will make much difference within reason.
I think that is it.

We have a couple of long threads which discuss whether some compounds are "better" than others, have a look at <"For Dan...spezial N..."> and there is a "magnesium nitrate" thread somewhere (like this one, but much longer <"Purer forms of .....">).

cheers Darrel
 

rebel

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I wondered whether the Ca/Iron and PO4 may precipitate??
 

dw1305

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Hi all,
I wondered whether the Ca/Iron and PO4 may precipitate??
They will, that was one of the reasons for keeping the solutions separate and acidified.

Keeping iron (and phosphate) in solution for hydroponics was one of the difficulties that led to the development of chelators. Originally citric acid (C6H8O7) was used, before the development of EDTA etc.
it was the recipe in the book I was given.
I still have it, and there is an E version - Hewitt, E. (1966) <"Sand and water culture methods used in the study of plant nutrition">.

cheers Darrel
 

AlexVojProc

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You can make an iron EDTA solution (using the sodium EDTA salt and iron sulphate),
This is how I'm doing it at the moment: I react 0.5M free acid EDTA, which is insoluble in water, with 1M sodium hydroxide, then continue adding sodium hydroxide until the pH is around 8, and at that point all the EDTA dissolves. Then I add the 0.5M Na-EDTA to 0.5M iron(II) sulfate, giving me 0.5M Fe-EDTA. I then do some maths to get the tank concentration to about 0.5 mg/L Fe.

Hi all, They will, that was one of the reasons for keeping the solutions separate and acidified.
From the short time I've been doing this, I agree that keeping all the solutions at a low pH (I use a *little* bit of sulfuric acid) and separated is the best way to avoid precipitation.

What's important to know is that dosing more than the standard concentration does no harm, other than the rise in TDS, but neither it it really necessary
Good to hear, thanks.

I used to make it up a separate micro-element solution, you don't actually need EDTA, you can use water and just acidify it to stop precipitation. One batch of micro-element solution would last me years. If you PM me your email address I can send you an excel file with the workings for making up the micro element solutions etc.
I'll PM you. It'll be interesting to see how similar our trace element concentrations are.
 

AlexVojProc

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After quick looking around, I found this in Tom Barr's "Confusion about EI and other myths":
18. Hoagland's modified solution is very rich and is a non limiting nutrient solution. EI is just a similar idea but on the lower end for aquatic plants, above the limiting ranges but not nearly as rich.
Hydroponics and Hoaglands solution has a very long history and test/research background for support.

As has already been mentioned, it seems hydroponic solutions like the Hoagland have similar effectiveness as EI. Am I correct in thinking that the inclusion of calcium nitrate and magnesium sulfate negate the need for a GH booster?
 

X3NiTH

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Am I correct in thinking that the inclusion of calcium nitrate and magnesium sulfate negate the need for a GH booster?

Yes, although I found that trying to make a concentrated solution for dosing using the above two caused problems in the bottle, at first all salts went into solution but within an hour all the calcium had precipitated out to calcium sulphate.
 

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