If this is a pool filled with chemicals to keep it fresh for swimming that might be an issue.
He could have picked up an intestinal parasite if the pool is not treated too.
As this has gone on for five days you need a vet to see him and check his bloodwork, a stool sample, and see if he is showing signs of internal infection or other illness.
This could be so many things from parasites to heart or kidney or liver issues that the best bet is seeing a vet. Its obviously not going to cure itself so its time for an in person exam.
Hope this helps you!
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