Continued from page 1
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
Case Study #1
Initial conditions as of November 1993: 500L aquarium with undergravel and canister filters; 240W fluorescent lighting, 12 hours per day; 15W UV sterilizer; 8cm 2mm gravel with a few laterite balls; no CO2 additions; no fertilizer; about 40 3-12cm fish; water temperature 27C, pH 7.5, GH 100ppm, NO3- 50ppm, 25% change every week; planted mainly with Hygrophila polysperma and Vallisneria gigantea, with a few Echinodorus sp., Cryptocoryne sp., and others.
The aquarium was purchased second-hand as a complete set-up and had been in operation at least six months prior to being acquired by the author [Conlin]. About a month after after being moved to the author's residence, a dense coat of green algae developed on the gravel-coated glass-fiber backdrop. Plant growth was marginal, even for the H. polysperma, which had small 3cm leaves and was not spreading. Hygrophila difformis was introduced and promptly lost its lower leaves.
Change: Twenty Terrapur cones were embedded in the substrate and Sera liquid fertilizer was added as directed to the tank water during water changes. Hydrocotyle leucocephala was introduced.
Effect: Growth of H. polysperma, H. difformis, and V. gigantea improved but long strands of green thread algae started growing on the backdrop. Various Echinodorus and Cryptocorynes showed marginal growth. The H. leucocephala quickly degenerated, leaving a few small fragments growing at the surface. Some red algae was noted on the leaves of Anubias barteri var. nana and along the leaf margins of the V. gigantea. After a few months, blue-green algae (cyanobacteria) began to cover the gravel and some plants.
Change: Erythromycin sulfate was added to the water at approximately 3.2mg/L.
Effect: Cyanobacteria disappeared for several weeks but eventually returned.
Change: Less food (particularly frozen bloodworms) was offered to the fish and a DIY yeast CO2 system was connected to the tank.
Effect: Cyanobacteria remained. Nitrates were unmeasurable. Plant growth was noticeably faster. Depending on the state of the yeast reactor, tank pH varied from 6.8 to 7.5.
Change: The Sera fertilizer was eventually discontinued on the assumption that it was contributing to the growth of the cyanobacteria. It was replaced with a commercial iron-containing trace element mix (initially 1/8 tsp of powder a day, soon increased to 1/4 tsp a day).
Effect: Nitrates rose to about 20ppm. Green algae began to replace the blue-green algae on the plants and gravel. An iron test kit indicated the presence of iron at a concentration below the first level on the color chart (0.25ppm). Plant growth accelerated, but the leaves on the H. polysperma became bent and the lower leaves fell off. This was assumed to indicate a potassium deficiency [4].
Change: K2SO4 was added to the tank at the rate of about 1/4 tsp/day.
Effect: Shortly thereafter the nitrate level became unmeasurable, leading the author to conclude that nitrogen was now the factor limiting plant growth.
Change: KNO3 joined the list of fertilizers being added to the tank on a daily basis. To simplify dosing, the trace elements, K2SO4, and KNO3 were incorporated into a liquid fertilizer. The mixture was adjusted to keep the nitrates at about 10ppm when the enough liquid was added to the tank (about 12mL) to keep the iron at an estimated 0.1ppm.
Effect: At this point, growth of the H. polysperma, H. difformis, and V. gigantea became exceptional, requiring weekly trimming. Somewhere along the line, duckweed had been introduced to the tank and it now began to clog the surface. Cryptocorynes and Echinodorus began growing new leaves every few days and sending out runners. Algae of all sorts quickly declined to the point where careful observation was required to find it. Strangely, the Echinodorus were unusually pale in color despite iron fertilization. Magnesium deficiency was suspected.
Change: Epsom salts were added to the fertilizer mix.
Effect: Within a few days, new Echinodorus leaves showed normal coloration.
Change: The yeast CO2 system was upgraded to a constant-flow tank/regulator/needle valve system.
Effect: Reduced pH swings (6.8-7.0). More free time for the author.
Change: After several months, during which plant growth remained excellent and algae scarce, four pellets of "Vigoro Super Triple Phosphate 0-48-0" (almost certainly Ca(H2PO4)2) were added to the tank as an experiment (approximately 0.1ppm phosphate).
Effect: The next day green spot algae was observed on the glass and Echinordorus leaves, followed two days later by blue-green algae that grew on some plants and driftwood. Duckweed soon required daily removal. Nitrates were unmeasurable several days after the phosphate was introduced but returned to 10ppm a week or so later (sadly, they weren't measured just before adding the phosphate). Two weeks after the experiment began, the blue-green and green-spot algae began to decline, and duckweed growth returned to normal.
Current status: Plant growth remains excellent. Some traces of algae still remain, principly green spot algae.
| Top | Back | Next |
 NetPets® Main Page |  The Fish Center |