Index

• Abstract
• Case Study 1
• Case Study 2
• Discussion
• Conclusions
• Recommendations
• Acknowledgments
• References
• Appendix A - Fertilizer Recipe
• Comments on this Paper
• Later comments on this Paper

Abstract

Experiments with planted aquaria appear to indicate that growth of green algae, red algae, and cyanobacteria is suppressed in planted tanks in which the availability of phosphate is the factor limiting plant growth. It is believed that when light, CO₂, N, K, and all micronutrients and trace elements are present in slight excess relative to the amount of phosphate available for plant growth, certain higher plants are able to out-compete algae and cyanobacteria for the phosphate in the water column, starving them of this essential nutrient. Two case studies are presented as evidence for this hypothesis.

Introduction

There are few things as frustrating to the aquarist interested in growing aquatic plants as algae. After spending a small fortune on lights, substrate additives, liquid fertilizers, and CO₂ systems in an attempt to get good plant growth, the aquarist is often rewarded with a lush carpet of algae. Unsightly and stubbornly resistant to eradication, the algae destroys the aesthetics of the tank while limiting plant growth by competing with them for light and nutrients.

In desperation, the aquarist experiments with various forms of algae control, including algicides, bleach dips, antibiotics (for cyanobacteria), physical removal, and the introduction of an assortment of algae-eating fish and invertebrates. Feed levels are reduced, light duration is decreased, and various combinations and amounts of fertilizer are tried, until through trial and error an uneasy truce is reached.

In the search for a solution, the aquarist is faced with an almost complete absence of information as to which of the many tank parameters should be altered in which order to eradicate algae already present while still maintaining favorable conditions for plant growth. This is hardly surprising given the huge number of variables, including light strength, duration, and spectrum; CO₂, micronutrient, macronutrient, and trace element concentrations; fish load; plant and algal species and density; and water chemistry and temperature. Sometimes the information that does exist appears contradictory; in [1], excessive growth of cyanobacteria is attributed to high nitrite and nitrate levels, yet this pest is often seen in fully cycled aquariums with no measurable nitrite or nitrate at all.

One option available to aquarists with deep pockets is to follow the proprietary Dupla system [2], a system of liquid fertilizer drops, tablets, tap water conditioner, substrate additive, and undergravel heating coils. Magnificent planted aquaria are routinely produced this way, but the components are expensive, the ingredients are not disclosed on the package (but see [3]), and little insight is gained into the relationship between plants and algae (or how the system should be "tweaked" for best results).

Like many others, the authors attempted to grow aquatic plants using typical aquarium configurations and various commercial liquid fertilizers and substrate additives. Frustrated by their inability to attain results even remotely resembling the photographs in the literature, they began systematically to add specific nutrients to their tanks and record their observations. Although eradication of algae was not the immediate goal of the experiments, it was noted that once the aquarium water was supplemented on a daily basis with trace elements, micronutrients, and the macronutrients K and N but not P, not only did the plants begin to grow extremely well, algae of all types began to die off rapidly.

In this paper, case studies of the authors' aquaria are presented. The case studies are followed by a discussion of the results in which a number of hypotheses are considered. These hypotheses are quite testable, and it is hoped that other hobbyists will be willing to perform controlled studies on their aquaria to either support or disprove them.

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