Plecostamus in an Outside Pond

Question
Hello, I have a large outside pond under an awning dedicated to Koi and I have kept a Plecostamus in the pond for the past ten years. He was a few inches long when I bought him and when I found him dead in the pond this morning, he was about 18 inches long. I can't think what may have killed him. All the fish are very healthy, well fed and the pond is well aerated. Can an anti algae powder kill a plecostamus. I use pond clear occasionally, but have been doing so for ten years with no ill effects. I am devastated and want to replace him with some small plecos, but want to avoid making the same mistake.I live in Botswana in Africa, no one here to help with this problem.
Many thanks in advance.  Sue

Answer
Hello Sue,
I'm sorry to hear about your loss.

Plecos naturally only live about 7 years in ponds and rivers, so he actually lived incredibly long for a pond pleco. I think it may have just been his time.

And for the record, algea killers can be harmful and even fatal to fish if too much is added. I doubt this is the cause though.