I had the opposite experience (as usual) in that GFO
clumped up and never lasted for me. I did a simple test using a reactor Carey recommended. 500 gallons of water, P4 was at .3ppm when I started, alk
was 11. I added 500ml of high quality BRS GFO
and started tumbling it. In 48 hours, no visible change to P4 but alkalinity went down to 8. 48 hours later, P4 was .25ppm and alk
had fallen to 7. That's when I stopped and slowly raised alk
back to 10.
I then replaced the GFO
with Phosgard. No other changes. In 48 hours alk
was still 10 and P4 was .1ppm. 48 hours later alk
was still stable and P4 was .03ppm. It has held steady there for the past three months. No clumping which is what reduced the usability of GFO
This is just what happened to me, your results may be different. I feed daily and have some messy eaters, so I needed to do something. This has worked brilliantly for me so far.
Sent from my iPhone using Aquarium Advice