I've always run water tests a couple of times a year since we've had this place. I was a little remiss in doing multiple tests in 2018 and 2019 but still was fairly well on top of my pond water chemistry nonetheless.
Every year, we stock RBT in late fall for the Project Healing Water folks. This year, I did a water sample in August and the alkalinity was the lowest its ever been. I normally add 20 tons of lime every 3-4 yrs or so when the alkalinity drops below 20 or so but this year I dumped in only 10 tons of lime (in 4.6 acre pond) late August because I feared a high alkalinity spiking that might adversely affect my upcoming RBT stocking. When I received my most recent post-lime test results, I am stunned that the alkalinity hasn't even budged while other test areas fluctuated wildly from the August test. Having seen the significant rise in alkalinity from previous liming, I am totally baffled by this. I've attached the spreadsheet I use to track all of my water samples so you can see what has happened in the past post-liming vs this latest round.
For reference purposes, I am using the same lab I have always used. Collecting the sample from pretty much the same area of the pond, ie between two aerators in the middle, I always have. The only small difference may be that I have typically used those TSA 4oz plastic liquid bottles you get at Walmart for my water samples. For the last two samples, Walmart was out of the bottles so I bought a four-pack from CVS and they were a different brand.
As for the lime, I have always used AgLime and purchased it from the same Co-op that I have always used in the past. I order it by the truckload. Before they arrive, I move one of my aerators close to the point on the lake. The spreader truck shows up, backs up to the point, and blows the lime out into the pond and the aerators help circulate it. Within 45 min- 1hour, the entire pond has a milky appearance and remains that way for a day or so.
A couple of questions...could I have some how contaminated one or both samples? I've never heard of a 'bad batch' of lime but is that possible?
Any other suggestions?
Thanks in advance for your responses and Happy Thanksgiving to all.