I am building a domestic solar hot water system DIY. Since I live in SoCal, I will be making it an open loop system with light freeze protection.I got a good deal on a set of used Novan Optima II 4x8 collectors. The concern I have is that I do not know the history of these (and neither did the seller), and I am worried that a toxic anti-freeze may have circulated through them in a past closed loop application. Keeping it simple, these are the questions I have:

1) Is there a simple and easy way to test (at home) what was previously used as fluid in the collectors?
2) If indeed a toxic fluid was used, is there a way to purge or cleanse the collectors so that they are appropriate for use on an open loop system?