I dilute mine even more than that, more like 1 mL to one liter of water. On a 300 gallon system I run 2 Liters/2mL of it every month to keep phosphate in check and GFO keeps in check throughout the month. I just like to target .03-.05 ppm as it's a mixed reef.
That being said, if it's not your only Phosphate export mechanism, assume 3 mL every couple weeks. 1 bottle is a Quart of 946 mL. 78 mL/year based on the above regimen and your looking at 12 years!
I'm currently adding 600 gallon DT and plan on dosing LaCl into my skimmer I picked up last weekend and then running a 10 micron filter sock on skimmer outlet so I'm sure precipitate is pulled out.