I wouldn't use the algaecide. Instead, manually remove the algae, and also increase the frequency and/or volume of your water changes.
As for the algae on the seahorses, you can gently brush it off with your finger, or gently blow it off with an eyedropper.
We need clear shots of the body, preferably from the side, to determine gender. I really can't tell from the two most recent pics, though it appears female. The pics in posts #1, 10, and 16 are of a female.