Thanks, Cary. I had just composed a post that was word for word the same as yours! :rolleyes:
Actually I'll just summarize my feelings on the subject.
1. If you just want to have a general idea as to your water clarity, go ahead and make a homemade disk. You can however, make a small effort to get the size and pattern down, so that if you're providing information to a biologist, the reading will be as accurate as possible. I'm one of those freaks who measures and speaks in metric, so I actually have to convert a lot of my posts to non-metric so you guys don't think I'm a nut.
2. I've found that the secchi disk is ideal for making measurements because the pattern makes it easier to see when the disk is very slowly spinning. It's easier to tell when it has officially disappeared from site because of the gentle rotation.
3. I'm weird.
Here's a quote from my favorite book in the whole world entitled "Fisheries Techniques".
...water transparency is commonly measured with a simple device called a Secchi disk. The disk consists of a circular plate (20 cm in diameter), painted black in two opposite quarters and white in the other two. To determine Secchi disk transparency, lower the disk into the water in the shade until it disappears and record the depth. Lower the disk a few feet and then slowly raise it until it reappears, and record this depth. The average of the two readings is the Secchi disk transparency. Make measurements at midday. Secchi disk measurements have been used in empirical estimation of the euphotic depth, the depth at which 99% of the surface radiation has been dissipated.
