It could be brown slime algea (Dinoflagellates) - golden brown gelaninous sheets or strings on substrate or glass, with trapped bubbles of oxygen produced by photosynthesis. Gambierdiscus toxicus is toxis to Turban snails common in new or biologically unstable aquariums.
Similar to: Diatoms, brown cyanbacteria, other dinoflagellates
Desirable/undesirable features: The toxic dinoflagellate blooms in aquariums under certain conditions, and blooms may last for weeks or months.
Controls: Let it run it course. Discontinue waters changes for the duration of the bloom. Boost alkalinity with buffers or calcium reactor. Use Kalkwasser for top-off water. Use activated carbon to reduce humic substances that promote dinoflagellate growth. The use of algal turf filters may limit dinoflagellate via competition for nutrients. Specific bacteria may also be used to control dinoflagellates.
Herbivores: Most herbivores will not eat dinoflagellates. Snails (Turbo, Astrea) may be harmed by them, rolling over and dying. Remove affected snails from the aquarium at once! Dead snails release nutrients back to the water that promote the algal bloom.
(From: Algea - A Problem Solver Guide)
