Do you test to determine when your GFO needs changing?
 

GFO: Phosphate remover, Granular Ferric Oxide.

For those who test, how often do you find it needs to be changed in your tank?

For those who don't test, what makes you decide when to change your GFO.

For those who don't use it... why not?

Despite owning a milwaukee digital phosphate meter which imo gives you a much more accurate reading then a test kit, I change my media every 2 weeks semi religiously. I used to be bang on, but have let up over the last few months. Sometimes letting it go an extra week or 2.

I choose 2 weeks because the media should still be working then. I can change carbon at the same time, and with bulk pricing it is affordable to just change it then instead of worrying if it's still good or not.

Similar experience... Despite having a LR Hanna colorimetre to test for Phosphate, I cannot determine with any consistency when to change out the GFO....so I change it every month.

In a continuing battle with cyano, I'm going to run larger quantity of GFO and see if that makes any measurable or visible difference. I'll also experiment with increasing the change frequency. From what I've read online, GFO has the capacity to absorb a lot of phosphate very quickly...but that might apply only to those with high phosphate levels to begin with.

My phosphate levels are always quite low, so it is likely the GFO lasts longer.

I've always been too cheap to buy a good PO4 test kit or meter. Recently I've gone from a 2 month interval to 1 month to see if I notice any difference. Since I have macro-algae in my sump, and very little algae in my display I assumed PO4 should be low in my tank... but I don't know.

One of the reasons I'm curious about this is despite having unmeasurable nitrates, and 400w bulbs the Purple Digitata in my tank is always brown. I wondered if phosphate may be the cause of this.

I've had a small bryopsis problem for the past year so I've been changing 1 cup of rowaphos each month (plus doing some other things). ATM my Elos PO4 test kit cannot detect anything but the algae is still there so I just keep changing out the media.

I quit using GFO, but when I did use it I changed it just before my tank looked like it needed changing. I figured that out to be about every 6 weeks.

I should mention other then nori my fish are exclusively fed frozen food which is why my phosphates are generally higher then the average person, thus the change every 2 weeks to be safe.

Interesting article from recent issue of Coral Magazine on feeding of cyano, that might help to understand better the persistence of cyano even in nutrition deprived environment.

I can't honestly say I've noticed a difference running GFO or not. So I stopped buying it.

What do other people notice about their tank with, versus without, GFO? Film algae on the glass? Water clarity? Etc.? Just wondering what people see, because I couldn't see a difference myself.

FWIW I've also never been able to get a non-zero PO4 reading on any test kit, or colorimeter I've used. Never. (And trust me I've gone through my share of test kits!!!) This makes NO sense to me, because I feed heavy, and don't do anything specific to mitigate phosphate.

This is one of the hugest question marks to me in the hobby.

When I started using GFO a couple of years ago, a red carpet algae (that's what I called it) that I had on my rocks (and snails etc.) for a year at least just melted away over a period of weeks. I was dancing in front of my tank (not a pretty sight). Over the same period my Chaeto did the same... but that's OK, fair trade.

Now I just use it as a preventative measure. If I slack off I notice my rocks aren't as clean.