The pond dating
Green Spot Algae is often eliminated with increasing phosphate levels in your water.
Try to maintain at least 0.3 to 0.5 of phosphates throughout the week and more preferable is in the range of 1.0 - 2.0 ppm of phosphates (however this algae is considered normal in small amounts).
As well, my methods may not work as well for some as all it often takes is new/different variable for an algae control method to be less effective.
Please note that algae control is NOT an exact science and there are many methods I have not used or researched that may also work.
In low concentrations they probably don't have any noticeable effect in aquarium systems, and indeed they are probably always present.
These diatom cells are encased within a unique cell wall made of silica (hydrated silicon dioxide).
What is also noteworthy is there is evidence of some diatom "algae" as a green colored slime like algae instead of the much more common brown diatom algae that is a common problem with new aquariums.
This has been called "Green Snot Algae" (scientific name Didymosphenia geminata) and is becoming more common in streams just under the surface and/or covering rocks (pictured to the right).
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Many of the methods cited here for algae control address the bio filter, but some do not and those that do should be used first based on my experience.