The buses are on
www.arrecifebus.com - but you will have to get one to Puerto del Carmen (€2.60 each way) and then change at the Biosfera for Calero. Can't remember how much that is unfortunately - but it won't be expensive... as it's then only €2.40 to Playa Blanca from PdC. Watch those timetables though... as the buses to PC aren't very frequent. Maybe Rich can tell you about the water taxi?
Journey from CT to PDC is about 40 minutes... then I'd guess 15-20 minutes to Calero. I'd get a taxi back to PdC from PC... and then bus back to CT from there. Someone mentioned a taxi from PC to PdC on here the other day (Desdamona maybe?) and I think they said €7... but I'm not entirely sure.
Elle xx