Lab conducted tests are by far the most accurate and they can test for many, many parameters that are not possible with a hobbyist Test Kit. However, THEY AIN'T CHEAP!! Most clients won't pay that kind of fee. I invested in a Bench Photometer and charge for water testing; less than half of what a lab would charge and the customers still fuss.
An interesting fact about algae, at least to me, is that the dominant specie of algae in a pond, especially larger ones, may change from year to year. This is also true, in many cases, of pond weeds.
Nature is amazingly intricate and dynamic and will befuddle and bewilder anyone who tries to outguess it, even the experts.