Red Leg,
I did some AI searching yesterday. One of the things I searched was food-grade dyes. (Which are obviously fit for human consumption.) It said there are some good blue dyes that might work for that application. I assume they will be quite expensive, but maybe worth you doing some additional research?
P.S. A few years ago, I contemplated building a cool-water fish species pond at my warm location. I speculated about buying some cheap tarps (or even super-cheap used bill board tarps - there is a current thread on those) and using those for shade. I would put the most reflective side "up".
They would quickly be destroyed in Kansas winds by any method of suspending them above the pond. So I figured why not float them? I would build some large rectangular frames with 3/4" PVC pipe to exactly fit the tarps I bought.
Floating them in the pond should reduce heat gain due to sunlight penetration, reduce evaporation, and they will probably develop a nice population of periphyton on the wet side of the tarp and pipes.
If the tarps are NOT reflective enough, you may need to suspend a portion of the tarp to create an insulating air gap. Leave a little give in your tarp attachments, and suspend some sealed jugs under the tarp to float a large percentage of the surface area. You could partially fill milk jugs, bleach jugs, etc. to get the exact amount of buoyancy you desire.
Just thinking out loud. You can probably come up with some better solutions that will match your specific requirements better.
Good luck on your pond project. I suspect lots of members envy you a little bit for having a pond that is too clear!
