when to replace GFO?

[baitrunner]

I'm new to GFO. Been tumbling it in a reactor for two weeks now. Phosphate has gone down from 3.0 to 2.0. I've read that most change out GFO every 3 to 4 weeks (approximately monthly). Since phos levels in my tank were so high to begin with, should I be changing it out more frequently until I have it under control?

 

[Captain smoke]

I would leave it and keep testing when levels stop dropping its time to change it out. You might have to change it out a couple of times to get it down to .03ppm but that also depends on your water volume

 

[ganjero]

At those levels (3.0) I would say daily or even twice a day. I would test the level at the output of your reactor and level of your tank, when the output level is equal to the tank's level your GFO has been depleted and its time for a change. However, you need to be careful if you have corals that have adjusted to these levels, bringing down the PO4 too fast could be detrimental.

 

[Reef Frog]

That's a very high level so it could be exhausting your GFO very quickly - perhaps days or even hours. It's hard to say. Testing & comparing the tank water to the output water is the only way to know for sure. The reagent tests are useful for discerning readings in the high ranges, but not so much for the lower ranges like <0.08 ppm, which can still drive algae growth. A low range meter is best for monitoring these low levels with better accuracy.

Later on, as PO4 levels drop, you may see clues with your eyes - growth on glass panes might return more frequently, or you might see a little more algae growing on the live rock for example.

 

[nuxx]

Normally any blip in PO4 or hint of algae is a good sign to change it.

If you're already way up there, then I'd say do it every other day depending on how much you're using.

Testing the output vs tank water is a good tip as well.