I'm not sure any Pharaoh tried to explain it that way but some scientists did put forth the theory a while back
according to this article in the Telegraph.
Many of the Biblical events that are described as acts of God, and which have been disputed by skeptics and/or non-believers for centuries,
could be explained by real natural phenomena. Whether they were God-directed is a matter of faith. I don't think science will ever be able to prove such claims.
But the word "miracle", used to describe many of these events, did not originally mean "an act of God". It just meant "something wonderful, unusual". In fact, magicians and false prophets are said to have performed miracles in various Biblical accounts. Unfortunately modern usage has left behind Biblical usage.
As for the Nile turning red, more than one theory has been proposed to explain it. And I believe there is a scene in "The Ten Commandments" starring Charlton Heston and Yul Brynner where Brynner (Pharaoh Ramesses) provides a "natural" explanation of why the Nile appeared to turn red (conveniently neglecting the fact that the water he had poured into the river turned red first, as presented in the movie).