A few questions about how you fly sparge:
- What water:grist ratio do you mash at?
- Do you add dilution water to the kettle? How much?
- How long does your sparge last?
My "strike" liquor to grist ratio is usually around 1.33 quarts per pound of grain. My usual sparge liquor to grain ratio is slightly less than 2-quarts per pound. The pH of my tap water is close to 6.0, but my water is weakly buffered. Any hot liquor that I use for a mash-out infusion is subtracted from my sparge liquor.
I rarely top-up a boil. I end up having to boil more than sixty minutes because I prefer to use a kettle that has at least a 1:1 height-to-diameter ratio. Most of my gravities run in the 1.054 to 1.062 range.
My current primary volume is 3.5 gallons (I built my latest brew house around this batch size). I usually collect around 5-gallons of runoff. My sparge runs about 30 minutes. I collect my run-off in two equal halves. I start heating the first half of while the second half is running. I mash in my house and boil on a 30K BTU propane stove in my garage.