I have heard of GFO causing burnt tips but I am not familiar with gfo myself.
Have you tried using Lanthanum Chloride for phosphates? I am not familiar with GFO but LC brings down phosphates in a couple of hrs or less. I dose it periodically and works great.
Where do u get Lanthanum?
Bleached tips usually indicate high ALK
Bleached tips usually indicate high ALK
+1 I would check your Alk first before blaming th GFO if you been running the same amount of GFO and have been changing it frequently I don't see this being an issue.