Wowee, thanks for all the advice.

Whilst I've got your attention....the BRS calculator also says to use 0.84 cups of carbon. Is this also way off base?

Thank again guys... Such a useful bunch

Dunc

Sounds about right.

Here's a pic of how many of my sps died(so did a bit of me) from using too much Gfo too fast. I now bleached and acid bath it and use It as extra filtration in my sump( very very VERY EXPENSIVE filtration)

http://i1292.photobucket.com/albums/...pshayec15u.jpg

1 tbsp per 30-50 gallons is a reasonable place to start. I've used this amount in a dozen different tanks.

wouldn't the amount you need and the frequency with which you replace it depend entirely on the amount of phosphate present in your system? I don't think there's a hard and fast rule for x amount per x gallons. If you add a small amount and you have lots of phosphate, your GFO will be exhausted within a matter of days (hours?), and will just be a bunch of rust tumbling in your reactor until you replace it, leading to very little visible difference in your corals or algae growth rates.

If you have almost no phosphate and you add lots of GFO, I doubt anything will happen in your tank, as the levels won't really change all that much. It will just take longer for the GFO to be exhausted.

I think people get in to trouble when they have high phosphate and add lots of GFO, in which case there's a massive, sudden drop. Whether or not this is true for you can be pretty easily determined by testing.

Asylumdown, I offered an amount that I've found safe to use in a variety of conditions. The trouble is that an aquarium can have a "zero" or near zero reading and still have a lot of phosphate within the aquarium depending which test kit a person is using. Using too much GFO can have major consequences.

Has anyone ever figured out why? I know lots of people have reported problems, but other than a sudden drop in PO4 levels, what else could GFO be doing? I've always been suspicious of GFO in general and think it can cause a few of the problems it's often employed to treat, but do you think that too much GFO is harming corals because of something it's adding to the water, or something it's removing?

i change out small amounts more often as oppsosed to larger amounts less often , as per what RHF recommends and has always worked great for me :)

i dont measure or weigh it out but i run maybe 1-2" in a tlf 150 reactor

i change mine out maybe every 2-4 weeks , i dont change it out so much based on the P04 test numbers but i can visually tell when my gfo is exhausted:)

I suspect that large amt pulls po4 too fast n the tank gets a big shock

be it small or large they would both pull out P04 based on the amount of water ran through them and how much they can pull depends on whats passed through and whats available.

for example a guy who fills a reactor and only runs it for 5 mins a day will most likely pull less phosphates than a guy who runs a much smaller amount and changes it every 24hrs;)

reason being is the amount of water passed through :)