This guy should not have used a pool LC solution. You might save a few bucks, but it is not worth it. You don't know the purity, composition, and other ingredients in the pool LC solution. He did a dilution based on 3rd party information, and his starting phosphate was not high 0.16ppm. So he may have either screwed up his calculations or the 3rd party information was wrong on how concentrated it was. And pool LC solution can also have contaminants or wide range of concentration as no one will notice when dumping it into a pool. I do feel if you bottom out on phosphates and continue to add LC, this is when it get a bit riskier for the livestock.
I recommend to either use the aquarium LC products. Or get lab grade LC powder and mix your own solution (but would only recommend for those that have experience doing this).