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brown algae problem
I've got a brown algae problem, and urgently need some advice. This
tank is an exhibit at a wildlife refuge that features native fish and
plants. I don't have daily access to it, and it's maintained by a
network of volunteers.
- 60g cold water tank populated with native fish and plants.
- Current fish load: 5 adult Pumpkinseed, 3 juvenile Pumpkinseed,
3 Banded Killifish, 4 Sheepshead Minnow, 5 Eastern Mudminnow,
and 1 Mummichog.
- Current plant load: mostly hornwort (Ceratophyllum echinatum).
Some Wigeon Grass (sorry, not had a chance to look up the Latin name.)
Hornwort doing very well, Wigeon grass OK. Used to have Low
Watermilfoil (Myriophyllum humile) but the brown algae stifled it
- Lighting is 2.5 watts/gallon using 4 Powerglo and 1 Floraglo
flourescent bulbs, each 30w (manufacturer is Hagen).
- Substrate is either dolomite or crushed coral. This used to be a
saltwater tank. When I inherited the project, we decided to retain
the substrate to keep costs down. (This may be the problem!)
- 25% water changes done weekly. Used to add Natural Gold fertilizer
but stopped doing it recently because of algae problems. Water source
was from a well on refuge property. Because we suspected high levels
of phosphates from agricultural runoff, we switched back to using
bottled spring water.
- Fish are fed 2x/day. Each feeding is 1/4 teaspoon flakes or
equivalent. They used to be fed once a day, but this was recently
increased. Algae also got worse, so this is obviously is one of
- Water tests as of last week show undetectable ammonia, nitrate,
nitrite, and KH. GH was moderate (sorry, forgot to bring in the
numbers), and pH was 8.5.
For the past 2 months, I've been playing around with various
parameters: changing fish load, changing amounts fed to fish, using
bottled spring water vs. well water, changing lighting, increasing
plants. Brown algae has been persistent. It recently got worse
probably due to increased feeding.
According to what I've been reading and from e-mail discussions with
an experienced aquarist, the primary source of brown algae is low light
and excessive silicates. In this case, the lighting is adequate. I'll
look for a silicates test at the aquarium store but doubt if that is
the problem because I cannot imagine where it's coming from.
The one thing that's not been closely examined is the substrate. The
calcium carbonate in dolomite or aragonite would increase the pH (it's
currently 8.5). My aquarist buddy mentioned that diatoms like higher
pHs. Could this be a factor encouraging their growth? Should I replace
the current substrate with regular gravel (small pebbles)? (It would
mess up the biological filtration some, but should not take long to
My apologies for the long post, but this problem is driving me totally
nuts. If you have any comments, or other suggestions, please e-mail
me at shireen at stsci_edu . I'll post a progress report if anyone is
interested in how this turns out...
Thanks for listening, and hope someone can help!
Shireen Gonzaga, Data Analyst, WFPC2 group, Space Telescope Science
3700 San Martin Dr., Baltimore, MD 21218, USA.
office tel.#: 410-338-4412, e-mail: gonzaga at stsci_edu