Glad you could join us!
The plecos should interbreed, if they're just color variants of the same species. I don't breed fish (intentionally
), but breeders I've talked to tell me inbreeding isn't a problem until about 7 generations.
I'm not sure what causes green spot algae, but it's pretty easy to remove with a good scraper such as Kent Marine.
BTW, you'll have a better chance of getting more responses to your questions by posting them in the right forums. Some people don't read introduction threads.