I have a cyanobacteria problem. I am using PhosBan/Phosguard as a filter medium and it doesn't really work that well, shall I worry of getting a GFO reactor or am I good with how it is? How would GFO be different?

my setup:

  • 30 gallons tank
  • 5 cichlids about 3-4 inches long
  • Fluval FX6 running all the time (bottomfloor is clean)
  • 1 feeding a day, with 1 pinch of cichlids food
  • air at high flow with long diffuser
  • some sunlight in the morning for about 2 hours
  • some plants struggling to grow
  • plant lamp on a timer from 2 pm to 8 pm
  • over the wall topfin filter with PhosGuard medium, changed every 2 months
  • tap water with primer + seachem additives changed 1 time a week

problem is the green patches on the rocks and glass that are hard to scrub off, and it keeps spreading

it used to have brown algae all over and little cyano here and there until i started using PhosGuard

now brown algae is gone and it's just cyano and it spreads like a wildfire

  • 2
    please clarify you have a 115liters tank and uses the fluval fx6 a filter that have a max flow of 3500liters hr.it is very hard to avoid algae if the tank gets any sunlight,it is very hard for plants to grow when you remove theCO2 by aeration and powerful filtration. Mar 16, 2019 at 5:50

1 Answer 1


GFO is a lot cheaper if you buy it in bulk which is why I would personally recommend it over other proprietary PO43- absorption mediums. I also have to agree with @Manuki, can you describe what problem you're having and the tank setup including age, lighting including the schedule, stocking, and what you have for water movement?

I don't typically recommend jumping straight for GFO or any other PO43- removal medium for cyanobacteria because it's usually a combination of issues that are causing it, which may be evidenced by the fact that phosban isn't working for you.


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