There are several planted aquarium commercial fertilizer “lines” of several products, all designed to be used together in a “program”. Easily 80% of the “fertilizers” in “programs” are pure unadulterated snake oil designed solely to get you to part with sizable chunks of money. The remaining 20% can be made DIY for about 10% of the cost of buying retail. I have little use for any of them. But if you are interested read on. This article is only for real nerds like the author.
Probably the best way to look at this is to examine what is probably the most complete “line” of fertilizers for aquarium plants, namely the Seachem “program” or product “line”.
Seachem Aquarium Fertilizer “Program”
It is instructive to examine the Seachem “program” or product “line”.
One should note that in all honesty I intensely dislike the “pseudoscientific bedazzlement” of Seachem’s marketing hype of its often very ineffective and over-priced products. So there is a definite admitted bias on my part against Seachem. I can’t help it. Also, note that Seachem threatened me with a libel suit. I don’t like to be threatened, even if it is an empty threat (you can’t be sued for telling the truth).
Seachem Flourish Products
Seachem makes a whole line of very overpriced and in many cases useless products for planted tanks. It is advantageous to look at each of these products. They are:
- Flourish™
- Flourish Trace™
- Flourish Advance™
- Flourish Supplement™
- Flourish Nitrogen™
- Flourish Iron™
- Flourish Potassium™
- Flourish Phosphorus™
- Flourish Tabs™
Note that Seachem had an “Aquavitro” line of products which are simply the products above with a higher price tag. We will ignore those products.
Let’s analyze each Seachem “plant fertilizer” product:
Flourish™
Per Seachem:
“Flourish® is a comprehensive plant supplement for the natural freshwater aquarium. It contains a rich assortment of important micro elements, trace elements, and other nutrients. These include calcium, magnesium, iron, and other important elements that are beneficial to aquatic plants.”
This is a very dilute solution of “Potassium Chloride, Calcium Chloride, Copper Sulfate, Magnesium Chloride, Ferrous Gluconate, Cobalt Sulfate, Magnesium Sulfate, Manganese Sulfate, Boric Acid, Sodium Molybdate, Zinc Sulfate, Protein Hydrolysates”.
This product simply makes no sense at all. Only if one is using distilled or RO water is this necessary. Almost all tap waters will have adequate supplies of everything in here save the potassium and possibly the iron. And a pinch of potassium bicarbonate will supply far more potassium at 1% of the cost of this product. Iron should be added at the roots, not in the water column. And Protein Hydrolysates will be fuel for heterotrophic bacteria in the water column and produce bacterial blooms.
If one wants to add iron and other micronutrients into the water column simply add one-tenth gram or just a “smidgen” of iron sulfate and a TINY smidgen of a micronutrient mix from your garden store to the one and a half liters. Put a squeeze in daily. Easy! (and Cheap!). Note that horticultural iron sulfate has a host of micronutrients in it as it is relatively impure. So one ONLY needs the ferrous sulfate.
Flourish Trace™
Per Seachem:
“Flourish Trace™ supplies a broad range of trace elements demonstrated to be necessary for proper plant health and growth. Trace elements are normally depleted by utilization, oxidation, and precipitation. The latter two processes occur more rapidly than with other micronutrients. This makes it important to restore trace elements regularly”.
This write-up is typical of the pseudo-scientific bedazzlement so typical of Seachem. This Seachem product adds very tiny amounts of some micro-nutrients to the water column which plants can get from 99.999% of all soils and waters in the world just fine. This is another useless, expensive Seachem product.
One must understand, that plants only need micronutrients in parts per billion concentrations (in some cases parts per trillion). Hobbyists talk all the time about parts per billion as though that is some substantial number. It is NOT. One part per billion is eight people on the face of the earth out of the entire population of the earth. So most soils and tap waters in the world have more than adequate amounts of all these elements. And plants cannot use them up nor is oxidation or precipitation any problem in virtually all soils.
If one wants to add iron and other micronutrients into the water column simply add one-tenth gram or just a “smidgen” of iron sulfate and a TINY smidgen of a micronutrient mix from your garden store to the one and a half liters. Put a squeeze in daily. Easy! (and Cheap!). Note that horticultural iron sulfate has a host of micronutrients in it as it is relatively impure. So one ONLY needs the ferrous sulfate.
The Actual Science of Micronutrients
What hobbyists fail to realize about micronutrients is that micronutrients (with the notable exception of iron, which I contend should not be a micronutrient) are present in more than adequate amounts in virtually all soils and all waters in the world.
Here is an example of the micronutrient needs of crop plants from agriculture. The numbers are quite applicable to all plants:
So Manganese uptake by corn and soybeans is roughly half a pound (like a few handfuls) spread over an entire acre of land. An ENTIRE ACRE! This is a very small amount of manganese.
If one wants to add iron and other micronutrients into the water column simply add one-tenth gram or just a “smidgen” of iron sulfate and a TINY smidgen of a micronutrient mix from your garden store to the one and a half liters. Put a squeeze in daily. Easy! (and Cheap!). Note that horticultural iron sulfate has a host of micronutrients in it as it is relatively impure. So one ONLY needs the ferrous sulfate.
I can find no research that supports any addition of micronutrients other than iron. Note that many of the chemical fertilizers used in the homemade recipes listed elsewhere are natural products and have significant levels of micronutrients. Triple phosphate and plaster of Paris specifically have all the micronutrients necessary for plant growth.
Many are concerned about micronutrient toxicity if one uses a micronutrient solution. These concerns are not warranted by the math. For instance, a level of 10 parts per million of manganese becomes toxic to some plants (“The Physiology of Manganese Toxicity”, Horst, W.J. 1988).
The manganese level in Flourish Trace™ is 85 parts per million in the bottle (8.5 x 10-8). The directions are “Use 1 capful (5 mL) for every 80 L (20 US gallons) twice a week“. The calculations are 5 ml is 0.0013 gallons. 0.0013/20 = 0.000065 (6.5 x 10-5). then (8.5 x 10-8) X (6.5 x 10-5) = 55.25 x 10-13 . This is a concentration of manganese in the aquarium water of 0.0000055 parts per million per application. The math become 10 divided by 0.0000055, which is 200,000. So to get to 10 parts per million one would need to dose 200,000 times. Not exactly something to worry about.
Flourish Advance™
This is what Seachem says about this product:
“Flourish Advance™ is an all-natural, biologic growth enhancer for aquatic plants. Its advanced formula contains phytohormones, minerals, and nutrients that dramatically stimulate the growth of both roots and shoots in aquatic plants. Phytohormones are a group of naturally occurring compounds that play crucial roles in regulating plant growth in a wide range of developmental processes, including cell division, formation and activity of shoot meristems, induction of photosynthesis gene expression, leaf senescence, nutrient mobilization, seed germination, root growth, and stress response. Used regularly, it also enhances mineral absorption and improves disease resistance.”
As is typical with Seachem they mix good science with pseudo-scientific bedazzlement. Phytohormones are actual chemicals that plants produce to control their growth. But altering the growth patterns of vascular plants with phytohormones normally does NOT produce a more robust or a more attractive plant. The hormones might well produce leggy plants, distorted leaves or roots on stems and leaves. And phytohormones do NOT “enhance mineral absorption and improves disease resistance”.
Plant hormones are compounds made up of only carbon, hydrogen, oxygen and sometimes nitrogen. As such, they will break down relatively rapidly in a water solution and feed bacterial growth. So any true plant hormones that might be in this water based product initially won’t be there after a few weeks on the shelf.
The words “all-natural, biologic growth enhancer” are typical of the marketing hype on “natural products” and indicates a product that doesn’t do anything good. And what “minerals and nutrients”? This product is pure snake oil.
Flourish Supplement™
Seachem Flourish Supplement™ goes into the water column and is largely potassium, calcium, and magnesium. It is a very dilute solution, as are all the Seachem Flourish products. Most water has sufficient calcium and magnesium for most plants.
To add potassium it is best to add potassium bicarbonate (preferred), potassium chloride, potassium carbonate, or potassium sulfate, any of which can be easily purchased from Amazon. The best way to add potassium is the homemade soluble fertilizer described in the link below. And the homemade root tabs described below add calcium and magnesium to the substrate. These are much cheaper and more effective products.
Flourish Nitrogen™
Seachem Flourish Nitrogen™ is 1.5% nitrogen and 2% potassium fertilizer. The nitrogen in Seachem Flourish Nitrogen™ is 50% nitrate nitrogen and 50% urea nitrogen. Urea is a compound made up of several ammonia molecules and some carbon. It is what humans pee. Urea simply is broken down in the water by bacteria to roughly 99.9% ammonium and 0.1% ammonia (at a pH of 7.0) in two to four days.
Flourish Nitrogen™ is a very dilute solution. If one buys ammonium salts and potassium salts off the internet and adds a little pinch of these every few days you do the same thing at a MUCH lower cost. Or simply use the homemade soluble fertilizer outlined in the link down below.
Growing plants that have roots need both potassium and nitrogen in significant amounts. Adding potassium and nitrogen to the water column is much less damaging to the aquarium than adding phosphorus and/or iron to the water column. So if you do not want to go to the bother of do-it-yourself fertilizers and have money to burn this is probably a very useful option.
If one desires to duplicate this one can simply buy urea from the internet. One can buy 1.5 pounds for $15. This is about 1% of the cost of the Seachem product. Urea is broken down over 2 to 4 days into ammonia by bacteria in the aquarium, so it acts just like a “slow-release” ammonia. The equation is:
CO(NH2)2 (Urea) + H2O + urease → 2NH3 +CO2
But note that this slow release is NOT NEEDED with higher plants (all plants which are not algae).
One cannot mix up urea beforehand in a jar and add a solution every once in a while. The urea will decompose. So one has to add the solid form of urea. The math become 0.36 gram/100 gallons = 1 ppm. Urea is 50% nitrogen. So for every ten gallons of water one needs to add 0.072 grams of urea to get 1 ppm. This is not a lot. If one wants to keep a 50-gallon tank at 1 ppm ammonia one will need about 1.5 grams (0.072 x 5 x 4) of urea twice a week. This is one-fourth a teaspoon (a level teaspoon is 6 grams).
Humans urinate urea, so human urine can be used to fertilize an aquarium. Urine averages 2% urea. So one needs roughly 75 grams of urine or one-third of a cup of human urine added twice a week. The big problem here is that the concentration of urea varies a huge amount depending on how much a human is drinking. This makes it difficult to control. And of course, this is just plain kind of gross.
Flourish Iron™
This product is 1% ferrous gluconate (ferrous gluconate is 11% iron by weight). It adds 0.11% iron to the water column. A MUCH cheaper alternative is to use iron sulfate from the garden store. It has to go into the water column, which is not ideal.
In well-oxygenated water above 7.5 pH, the soluble form of iron (ferrous iron, Fe+2 [Fe(II)]) in most fertilizers is oxidized relatively rapidly to the very insoluble form of iron (ferric +3 Fe+3 [Fe (III)] hydroxides). The ferric hydroxides cannot be utilized by the plants very well. Alkaline high pH ferric phosphates are even more insoluble and unavailable.
In substrates, there is less oxygen so the iron can remain ferrous much longer. In organic soil substrates, the oxygen level is typically somewhat low and the pH is typically lower (6.0 to 7.0 pH) so iron is rarely a problem.
If one wants to add iron and other micronutrients into the water column simply add one-tenth gram or just a “smidgen” of iron sulfate and a TINY smidgen of a micronutrient mix from your garden store to the one and a half liters. Put a squeeze in daily. Easy! (and Cheap!). Note that horticultural iron sulfate has a host of micronutrients in it as it is relatively impure. So one ONLY needs the ferrous sulfate.
Note that the previous paragraph has been repeated four times now in this article. Seachem really milks the iron/micronutrient angle for all its worth. That is simply because most people don’t really understand what the term “micronutrient” means.
Flourish Potassium™
This adds a dilute solution of potassium to the water column. Potassium in all its forms is very soluble so adding it to the water column makes sense. But this 5% (NPK of 0-0-5) solution of potassium is very high priced. A pinch of potassium salts obtained from the internet is much cheaper. To add potassium it is best to add potassium bicarbonate (preferred), potassium chloride, potassium carbonate, or potassium sulfate, any of which can be easily purchased from Amazon. In high-tech, CO2-injected tanks one can use potassium nitrate.
Flourish Phosphorus™
Flourish Phosphorus is simply an overpriced, weak solution of potassium phosphate with an NPK of 0-0.3-0.2. It is a solution added to the water column, which is not what I would recommend. It is much better to add phosphorus to the roots of the plants. And the easy alternative is to simply buy some potassium phosphate over the internet and add a smidgen of that several times per week to the aquarium water. It is a LOT cheaper!
Seachem “Program” Cost
The above eight products have a “program” of twice-a-week adds per the Seachem website. The cost of adding these eight Seachem supplements to an eighty-gallon high-tech planted aquarium is $105.84 upfront which will last six months. The cost over five years is $1,058.40. The cost of the chemicals used to make the homemade fertilizers is $45.62 up front and the chemicals will last at least five years and probably more than ten years.
$45.62/$1,058.40 = 4%. I.e., the profit margin here for Seachem is an obscene 96% if you keep the aquarium for five years. If you keep the 80-gallon aquarium for ten years and use homemade fertilizers you will save $2071.18. HHHhhhmmmm ….. Interesting …..
Flourish Tabs™
Flourish Tabs™ are small fertilizer tablets that are supposed to be put into the soil around each plant. All the experts agree that the phosphorus and iron fertilizer that rooted aquarium plants need is best added in the form of small root fertilizer tabs which are pressed into the soil layer around a plant.
Seachem Flourish Tabs™ contain Calcium 14.9%, Sulfur 12.2%, Iron 2.2%, and a host of “micronutrients”. Gypsum (calcium sulfate or Plaster of Paris) and iron sulfate would appear to be the major ingredients of these tabs. This makes Seachem Flourish Root Tabs™ an iron fertilizer tablet only. This is a reasonable product and I would use it and recommend it. Thus out of the nine Seachem products in their fertilizer “program” I have use for one and only one.
Seachem does not make a slowly soluble calcium sulfate-based tab fertilizer that contains phosphorus. This is unfortunate as tabs are a better way to supply phosphorus. I recommend Aquarium Co-op tabs or homemade tabs to supply the phosphorus.
ADA Dosing
ADA’s liquid fertilization system 1 (sometime called “lean fertilizing”) is another fertilizer “program”. The ADA fertilization method is very expensive and I do not recommend it. The ADA system relies on ADA Aqua Soil Amazonia as a substrate, while the amount of nutrients dosed into the water column is far leaner.
The ADA Aqua Soil Amazonia is an incredibly expensive substrate that appears to simply be baked peat and manure-enriched clay soil which has been broken up. It appears to have been baked at a relatively low temperature so the soil properties remain. But I suspect a Walstad or Father Fish soil layer with some composted manure and some peat under an inch of gravel or large grain sand would do the same thing at a much lower cost,
The ADA fertilizer water column dosage is high in potassium and contains iron, but contains much smaller amounts of NO3/PO4. Many of such tanks will measure 0 ppm NO3 in their water column when water is tested. Plants will mainly draw their nitrogen supply from the ammonia-rich soil. As the soil petters out (6-12months), such tanks become naturally nitrogen-limited and growth slows down (which may not be a bad thing). Additional new soil & root tabs are typically added to enrich the soil as it ages.
A weekly cumulative dose of nutrients using ADA’s liquid fertilization system1 would give approximately:
- Nitrate as NO3 – up to 0.7ppm mix of NO3/NH3
- Phosphate PO4 – up to 0.6ppm
- Potassium K – up to 25ppm
- Iron Fe/traces – up to 0.06 ppm
This system is relying on nitrogen and phosphorus coming from the very high-priced Aqua Soil and/or fish. This is not a system I would use. I refuse to pay huge sums of money for something that has what appear to be some very exaggerated marketing claims.
Note there are MANY commercial soils made for planted aquariums. They all share one characteristic, they are obscenely expensive. There is a fallacious argument often made that “you get what you pay for”. In this case, it just isn’t true. None of these soils is any better than soil from your local garden store.
Fertilizers in More Depth
We go into aquarium fertilizers in more depth in the following links:
15.5. Aquarium Fertilization
15.5.1. Ready-Made Fertilizer
15.5.3. Estimative Index
15.5.4. NH4 + Tabs Fertilizer
15.5.5. DIY Epiphytic Fertilizer
15.5.6 Fish Food as Fertilizer
15.5.7. DIY Fertilization
Startpage Aquariumscience
Source: Aquariumscience.org – David Bogert
