Just to update on what happened and what I did.

I got some better test gear, a pool test kit instead of just test strips. It turns out that the test strips aren't very accurate. My pH fluctuates from 8.0 in the afternoon to 7.6 or so in the morning versus a costant 6.8 reading with the test strips. My alkilinity is 25 ppm rather than 30-40 ppm measured on test strips and total hardness is only about 60 ppm vs 100+ measured with test srtips. I believe the titrations much more than the strip readings.

As the water in my pond warmed this weekend , I got up to 22 inches of visibility on a Secchi disk which I felt like was plenty to proceed with fertilizing. I am guessing the combination of the gypsum I added to the pond and phytpplankton activity are the reason the visibility has increased so much in the past week or two.

I also removed an estimated 10 lbs of filamentous algae from the pond surface with a pool skimmer before I feertilized. The FA was not out of control but I felt like it was better to be proactive than have a big problem post fertilization.

I fertilized this afternoon with a gallon of 10-34-0 inorganic liquid fertilizer. I diluted the gallon of fertilizer with 15 gals of pond water and distributed it over the approx 1.8 acres surface area of the pond in my trolling motor propwash. The fertilizer called for a gallon of fertilizer per surface acre but I want to go slow and see what happens. I feel like you can't undo it once you fertilize so am taking baby steps. I'm shooting for 15-18 inches of post fertilization visibility.I'll let you know how it turns out.

I'm planning to add a few tons of limestone to the pond between now and next spring. I want to try to get my alkilinity up above 30 to feel more comfortable that ph swings won't be an issue.