Do you test to determine when your GFO needs changing?

[Reefer Rob]

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.

[whatcaneyedo]

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.

[Myka]

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.

[corpusse]

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.