Aquarium Plant Nutrition

by Robert Fenner
Reprinted with permission, from Bob's website in San Diego: www.wetwebmedia.com
Aquarticles

Planted aquarium systems and their owners fall into two categories by their actions and philosophy. Extensive types take the 'natural' route of moderation: easy lighting, some attention to soil and substrate nutrient input, and "fish food fertilization". Intensive folks blast their set-ups with high intensity illumination,
regularly feed in chemical supplements, infuse CO2, forever tinkering with gear and test-kits.

Both approaches "work" for aquarists conscientious enough to study and apply adequate knowledge. Extensive ways are slower and less spectacular; intensive methods are more sure-fire, expensive and luxuriant in results; both are patently not-natural.

"Wherefore Art Thou, Essential Nutrients?"

Living aquarium plants require the same 16 elements as terrestrial plants; two of them, hydrogen and oxygen are obviously readily available. It is up to the aquatic gardener to provide the other fourteen in usable forms and concentrations, under appropriate ranges of environmental conditions (e.g. pH, temperature, lighting) to promote plant growth.

Will you have to don a white lab coat and spend your days investigating the chemical, physical and biological interactions that are conducive to plant aquariculture? Nope. As with an operational understanding of working an automobile (put in gas, check tire pressure, etc.), such success is to be had by some basic understanding and maintenance.

And with proper set-up, the task is even less daunting! As you will find, there is no great consensus on whether to adopt intentional supplementation. However, for almost all situations, minimum nutrient requirements are met through water, substrate and fish food feeding.

Here we'll present an overview on the major, or macro-nutrients, those of smaller concentration, the minor or micro-nutrients, sources and factors influencing their availability.

The Major Mineral Nutrients of Plants

As for the label on "complete" terrestrial fertilizer bags the first three elements necessary to aquatic plants are N, P, K, Nitrogen, Phosphorus & Potassium. To these you can add Carbon, Oxygen, Hydrogen, Calcium, Magnesium, Sulfur and I'll throw in Iron.

The Minor, or Micro-Nutrients:

Include Zinc, Copper, Manganese, Molybdenum, Boron, Chlorine, and possibly sodium.

Factors Influencing & Providing Nutrients:

The abundance of all nutrients for aquatic plants in the wild has been noted many times in the literature (Horst). Likewise, the availability of all chemical needs from foods (Walstad), as well as contributions from various waters, mineral substrates (gravel, sand), and soils.

In captive systems all these source mechanisms interplay to provide essential (and not) media in differing proportions. The conscientious aquatic gardener is aware of origin contributions, testing; adjusts for the same through water changes, possible supplementation.

But the presence of essential materials in agreeable proportions is not the end-all of considerations; other factors, light, temperature, pH, dissolved oxygen and more figure into the form and usability of these materials by living plants.

How do these materials make their way into photosynthetic life? Plants absorb water and carbon (as carbon dioxide) in molecular form; all other essential nutrients as charged ions. There is evidence that plants can effectively deposit the necessary heavy metals (e.g. iron) and even absorb undissolved nutrients
from the substrate.

Here are some of the 'highlights' in contributing sources and factors affecting plant nutrients.

Water:

"It's the water, and a lot more". Depending on your water source, use of reverse osmosis, deionization or even distillation, your mains or tapwater may play a significant role in providing mineral nutrient to your aquatic plants. The water authority or other agency involved in this utility can provide you with an analysis of what's to be expected in your tap.

Some aquarists prefer to start with water that has had most everything other than the water itself removed, and add back their desired solids. For most localities and set-ups this is unwarranted; other less-extreme steps to ameliorate hardness, etc. being simpler and less expensive.

Fish Foods:

Also known euphemistically as "organic fertilizer". With minimal fish stocking and outside feeding of fresh and prepared foods, almost all systems receive enough of all necessary macro and micro-nutrients to support plant life. For rapid, sustained luxuriant aquarium plant growth, however, outside supplementation and soil addition are called for.

Substrates and Soils:

These topics are too wide for complete treatment here. Please see other pieces in this series for elaboration.

Basically, substrate (sand, gravel) acts in three ways, as a mineral source, anchoring media, and bio-habitat in aiding or denying plant growth. The proper size, depth, shape and composition of substrate is therefore of consequence.

Soil(s) make available organic and inorganic nutrients, act as catalysts, and support the interstitial bio-chemico-habitat. The benefits of their appropriate use are undeniable. Cation exchange provided by clay particles' negatively charged sites temporarily hold and make available positively charged ions (e.g. Ca2+, K+, Na+). This is why some clay is essential in aquarium soil.

Light and Carbon

Sufficient quantity, quality and duration of light are obviously fundamental; as is adequate carbon, generally measured as CO2. Without these inputs, no photosynthesis, no plants.

Carbon dioxide plays another intimately important role in alkaline-carbonic pH balance. Much more about this in a later article. For now, here are some very useful Internet links to CO2 use/gear:

http://www.wcf.com/
http://www.geocities.com/bwe407/poll_nn4.html
http://www.csd.net/~cgadd/aqua/diy_co2rig.htm
http://www.geocities.com/nguyenhg/

Temperature

The "average kinetic energy", aka thermal content of a system controls all rates of reaction, chemical, physical, and the sub-set within we call biological. Plants like animals, have optima and ranges of temperature tolerance. You are charged with knowing and accommodating your species mix to its regime.

pH & More:

The acidity/alkalinity of a system is a large determinant in the availability of nutrients for plant growth. Yes, this is a "plug" for monitoring, setting up and doing maintenance to produce the "dynamic equilibrium" of a steady, moderate substrate and water pH.

Placing and keeping pH is effected by substrate and filter media choices, water chemistry manipulation and exchanges.

Circulation & Water Changes

Movement in and periodic partial removal and replenishment of water aid in destratification, removal of accumulating "heavy water", promotion of redox potential, and replacement of minerals.

In the wild, currents, thermal and wind turnover, rain and runoff take care of these concerns; in captive aquatic forests, it's up to you and your filtration and mechanical circulation. Ideally water would be continuously entering and leaving your systems, making nutrients available in a consistent manner and carrying away undesirable material... realistically, weekly changes will approach suitable conditions; coupled with other (substrate, water, soil) factors.

Supplementation:

All the above taken into account, should you engage in chemical augmentation; liquids, granular fertilizers? Even CO2? For years before these innovations, aquarists kept splendid planted aquariums... many folks were not as fortunate however. With supplementation, success is practically guaranteed. What types
of supplements, if any, should you employ?

If you haven't heard it enough, NEVER USE TERRESTRIAL FERTILIZER IN AN AQUARIUM. Per the above spiel, you can see that these are too concentrated and wrongly formulated for aquarium use; too much fertilizer is dangerous, it will poison your system. This applies to all land-plant fertilizers, including organics like urea and bloodmeal.

The most widely available aquarium plant fertilizers are liquids and pellet/tablets. Liquids are ideal for floating and un-rooted plants and have the advantage of low and diffuse concentration; minimizing the likelihood of 'burn' and algal bloom. Tablets and pellets are better for their longer action and targeted placement for rooted aquatics.

All types of augmentation, fertilizer, soil, require periodic replacement. Liquids are best scheduled for weekly or more addition in conjunction with water changes.

All these forms of supplementation vary in their specific chemical formulations, and each has their league of supporters and detractors. I myself encourage using just an appropriate soil and occasional iron prep.. For the uninitiated, if you're so inclined, you are further urged to utilize a "complete" fertilizer, one with all macro- and micro-nutrients purposely included.

Know the products you are using and their limitations. In particular understand that there are interactions between the chemical species present and the ones you are adding. Once again, the value of frequent partial water changes can be seen as a mechanism for replenishing mineral salts and diluting excess dissolved solids.

Close:

Plants require a number of elements for metabolism and growth that they obtain from the water, soil (if any), substrate, cycled fish food, fertilizer (if added), and air. In nature most of these are provided by the weathering of rock; in aquariums, depending on the rate of growth desired, they're augmented on a periodic basis via the sources listed above.

The major chemical nutrients of land and aquatic plants are identical; the form and ways in which aquatics take them up however are different. These differences are important to the aquatic gardener in approaching methods of appropriate fertilization.

Should you utilize chemical supplementation? With most set-ups this is unnecessary to support growth. On the other hand, most luxuriant systems utilize soil, CO2,intense lighting, and chemical supplementation.

Bibliography/Further Reading:

Baensch, Hans A. & Rudiger Riehl. 1993. Aquarium Atlas V. 2. Rare Fishes and Plants. 1,212 pp. BAENSCH, Germany.

Fuchs, Lothar. 1975. Tips for the controlled fertilization of plants. ADI 3:4/75.

Horst, Kaspar. 1977. Aquatic plants; Interpretation of our field studies for use in the aquarium. ADI 4(1977), #18.

Horst, Kaspar. 1978. Tropical streams are being permanently fertilized. ADI1(1978) #19.

Jeffries, Owen R. 1990. Correct fertilization of tropical aquatic plants. FAMA11/90.

Jeffries, Owen. 1995. Substrate and liquid additives for improved plant growth in aquariums. FAMA 6/95.

Kassebeer, Gerd. 1988. An analytical course for aquarists; IX. Balance sheet of aquarium plant nutrients. Today's Aquarium-Aquarium Heute 2/88.

Kelly, Jim. 1996. Notes on key soil characteristics for aquarists. TAG 9(4):7,8/96.

Krumbholz, Paul. 1993. The Krombholz kronicles: mineral nutrition of aquatic plants. TAG 6(5):9,10/93.

Pedersen, Peter L. 1994. What about phosphates? TAG 7(1):1,2/94.

Pooler, Gene. 1996. Playtime in the fish tanks (On iron use). Tropical Breeze, bulletin of the San Diego Tropical Fish Society, Winter 96.

Raven, Peter H., Evert, Ray F. & Helena Curtis. Biology of Plants, 2nd ed. Worth Publishers, NY. 685 pp.

Spiers, Dale. 1991. Plant growth and iron. TAG 4(1):1,2/91

Walstad, Diana.1992. Aquatic plants prefer ammonium to nitrates. TAG 5(6):11,12/92, and FAMA 4/94.

Walstad, Diana 1993. Plant nutrient availability in the aquarium. FAMA 5/93.

Walstad, Diana. 1994. Fishfood as a source of plant nutrients. TAG 7(2):3,4/94.