If you get the bulk GFO it's not that bad, it's the process of getting phos levels down that burns through it quickly, but once it's down you don't go through that much. If you've had high phosphate for a while, you're going to have to keep changing the absorbing media until it stops leaching from your rocks, but once you're there, easy peasy. With levels that high, I'd bet you'll need to change your phos media every day to two days for a week or so just to get the levels down to the 0.03-0.00 range, and you'll probably burn through GFO faster than you'd like for the next few weeks-months, but it will eventually level out. Watch out for stress to your corals though, as sudden changes in phosphate levels isn't their favourite thing in the world.
And as stated, phosphate removing substrate such as GFO is a way better bet for phosphates than biopellets, unless you're starting with nitrate levels 16 times higher than your phosphate levels. Biopellets can only consume nitrate and phosphate according to the Redfield ratio of C:N:P at 106:16:1 The biopellets supply essentially a limitless amount of carbon, so it's the nitrogen phosphorous balance that you have to worry about in how effective pellets will be, with phosphorous being the least utilized molecule in the process.
In most cases (and yours, most likely), people have phosphate well in excess of the redfield ratio relative to nitrates, so after the biopellets reduce nitrate to trace/undetectable levels, they're left with the balance of phosphates that can only be brought down by GFO. I've been running Biopellets since day one, and without GFO, my phosphates can climb as high as 0.08ppm (tested by hanna), while my nitrates stay undetectable.
For the record though, even 1.2ppm phosphates in the hanna checker test vial (the highest I've seen with my checker) doesn't produce a colour change that the human eye can detect, so are you sure you didn't accidentally mix in some powdered plant fertilizer instead of the hanna reagent?
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